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Showing papers on "Excited state published in 1972"


Journal ArticleDOI
TL;DR: In this article, Levitt and Levitt developed a method for the consistent calculation of ground and excited state potential surfaces of conjugated molecules, which is based on the formal separation of u and 7r electrons, the former being represented by an empirical potential function and the latter by a semi-empirical model of the Pariser-Parr-Pople type corrected for nearest-neighbor orbital overlap.
Abstract: A formulation is developed for the consistent calculation of ground and excited state potential surfaces of conjugated molecules. The method is based on the formal separation of u and 7r electrons, the former being represented by an empirical potential function and the latter by a semiempirical model of the Pariser-Parr-Pople type corrected for nearest-neighbor orbital overlap. A single parameter set is used to represent all of the molecular properties considered; these include atomization energies, electronic excitation energies, ionization potentials, and the equilibrium geometries and vibrational frequencies of the ground and excited electronic states, and take account of all bond length and bond angle variations. To permit rapid determination of the potential surfaces, the u potential function and SCF-MO-CI energy of the r electrons are expressed as analytic functions of the molecular coordinates from which the first and second derivatives can be obtained. Illustrative applications to 1,3butadiene, 1,3,5-hexatriene, a,w-diphenyloctatetraene, and 1,3-cyclohexadiene are given. detailed interpretation of electronic transitions and A concomitant photochemical processes in conjugated molecules requires a knowledge of the ground and excited state potential surfaces. The determination of such surfaces has long been a goal of theoretical chemistry. Difficulties in a reliable a priori approach to the problem for a system as simple as ethylene2 are such that calculations for more complicated molecules are prohibitive at present. Consequently, a variety of methods that utilize experimental data have been introduced. Completely empirical treatments, in which the energy surface is expressed as a function of potential parameters fitted to the available information (1) Supported in part by Grant EY00062 from the National Institute of Health. (2) U. Kaldor and I. Shavitt, J . Chem. Phys., 48, 191 (1968); R. J. Buenker, S. D. Peyerimhoff, and W. E. Kammer, ibid., 55, 814 (1971). (equilibrium geometry, vibrational frequencies, etc.), have had considerable success in applications to molecules for which a localized electron description is app l i~ab le .~ The great advantage of this type of approach, which leaves open questions of reliability when extended from one class of molecules to another, is the ease and speed of the calculations; this had made possible applications to systems as large as certain nucleic acids and globular proteins. For conjugated molecules, however, the importance of delocalization introduces difficulties into such an empirical treatmenL5 (3) (a) See, for example, J. E. Williams, P. J . Stand, and P. v. R. Schleyer, Annu. Reu. Phys. Chem., 19, 531 (1969); (b) S. Lifson and A. Warshel, J . Chem. Phys., 49, 5116 (1968); A. Warshel and S . Lifson, ibid., 53, 8582 (1970). (4) M. Levitt and S. Lifson, J. Mol. B i d , 46, 269 (1969); M. Levitt, Nature (London), 224, 759 (1969). ( 5 ) C. Tric, J . Chem. Phys., 5 1 , 4778 (1969). Journal of the American Chemical Society 1 94:16 1 August 9, 1972

676 citations


Journal ArticleDOI
TL;DR: In this paper, the pseudocontact contribution to the NMR shifts for lanthanide complexes in solution is derived from the anisotropy in the susceptibility, provided that the molecular geometry is independent of temperature and of the lanthanides ion, the shift should vary as T−2 and in a predicted way from ion to ion.

540 citations


Journal ArticleDOI
TL;DR: In this paper, the photofragment spectrum of NO2 has been measured in the near ultraviolet at 28 810 cm−1 and at least two prominent peaks in the translational energy distribution were found to correspond to nearly equal probability of recoil with the NO fragment in the v=0 and v=1 vibrational states.
Abstract: The photofragment spectrum of NO2 has been measured in the near ultraviolet at 28 810 cm−1. A molecular beam of NO2 is crossed with brief pulses of polarized laser light and measurements are made on the distributions of speed and direction of the recoiling O and NO fragments produced by photodissociation. The average translational energy of the fragments is about 60% of the available energy. There are at least two prominent peaks in the translational energy distribution. We conclude that the two peaks most likely correspond to nearly equal probability of recoil with the NO fragment in the v=0 and v=1 vibrational states. Such vibrationally excited NO fragments produced by photodissociation in polluted atmospheres could perhaps react with different rates than ground state fragments. The positions and widths of the peaks indicate that there is a significant rotational distribution. Statistical and direct models for photodissociation energy partitioning are briefly explored, and their predictions compared wit...

409 citations


Journal ArticleDOI
TL;DR: The angular distribution of recoil of O atoms from the photodissociation of NO2 at 28 810 cm−1 was analyzed to obtain information about the lifetime and symmetry of the excited dissociative state.
Abstract: The angular distribution of recoil of O atoms from the photodissociation of NO2 at 28 810 cm−1 is presented and analyzed to obtain information about the lifetime and symmetry of the excited dissociative state. The theoretical effects on photofragment angular distributions of excited state symmetry, lifetime, angular momentum, and angular recoil distribution with respect to internal coordinates are considered. The actual angular distribution measured by photofragment spectroscopy, peaks in the direction of the electric vector of the light, indicating that the predominant upper state is of 2B2 symmetry. Some absorption leading to states of different symmetry cannot be excluded. An upper limit for the lifetime of the excited NO2 molecule before dissociation is ∼ 2 × 10−13 sec, indicating that break‐up is too rapid to be affected by collisions in the atmosphere where NO2 photodissociation is an important step in photochemical air pollution.

359 citations


Journal ArticleDOI
M.J. Rice1, W.L. Roth1
TL;DR: In this paper, a theoretical model for ionic transport phenomena in such super ionic conductors is presented based on the hypothesis that there exists in the ionic conductor an energy gap ϵ0 above which ions of mass M, belonging to the conducting species, can be thermally excited from localized ionic states to free-ion like states in which an ion propagates throughout the solid with a velocity vm and energy ϵ m = 1 2 M v m 2.

317 citations


Journal ArticleDOI
TL;DR: In this paper, the translational energy distribution of the photodissociation products is calculated from energy balance, and the distribution of fragment internal energy is then calculated, and two peaks are seen in these distributions for both methyl and ethyl iodide, corresponding to formation of ground and excited state iodine atoms.
Abstract: Photofragment spectroscopy has been applied to the photodissociation of methyl, ethyl, n-propyl and isopropyl iodide at 266.2 nm, both to study the process of unimolecular break-up of electronically excited molecules and to determine the energy distributions of the resulting excited fragments. By crossing a molecular beam with a powerful pulsed laser beam in high vacuum and monitoring the arrival times of the recoiling photofragments with a mass spectrometer detector, the translational energy distribution of the photodissociation products is measured. From energy balance, the distribution of fragment internal energy is then calculated. Two peaks are seen in these distributions for both methyl and ethyl iodide, corresponding to formation of ground- and excited-state iodine atoms. The fraction of the energy available after exciting the I atom which goes into internal excitation of the alkyl fragments increases from ∼12% for methyl iodide to ∼50% for the propyl iodides. Thus, the “hot” methyl radicals formed in methyl iodide photolysis are predominantly translationally, rather than internally, excited. The experimental results are disscused in relation to the processes involved in alkyl iodide photodissociation lasers. Dynamic models for energy partitioning in molecular photodissociation are compared with the observed data. The simplest statistical models predict much too high excitation in the alkyl radical. The measured results fall in between the predictions of direct impulsive models based on “rigid” and “soft” radicals, and thus a possible picture for the photodissociation of the alkyl iodides is quasi-diatomic excitation of the C—I bond, followed by recoil of the I atom and a partially deformable alkyl radical. An illustrative example is given of how one might use these unimolecular results in modelling the bimolecular reactions of alkali metal atoms with alkyl iodides, following the analogy drawn by Herschbach and co-workers between photodissociation and “harpooning”, i.e., electron transfer, reactions.

269 citations


Book
01 Mar 1972
TL;DR: The Luminescence of Organic Molecules and the Effect of Nuclear Displacements on the Emission Spectrum and Lifetime is studied.
Abstract: 1 Some Principles Governing the Luminescence of Organic Molecules.- 1. Introduction.- 2. Spontaneous Emission.- 2.1. Relationship Between Lifetime and Absorption Coefficient.- 2.2. Influence of Multiplicity on Observed Lifetime.- 2.3. Luminescence from Nearby States.- 2.4. Multiple-State Decay: An Example.- 3. Molecular Luminescence Characteristics.- 3.1. The Transition Dipole Moment.- 3.2. Spontaneous Luminescence in Aggregates.- 4. The Adiabatic Approximation.- 4.1. Dependence of Transition Moment on Nuclear Displacements.- 4.2. Effect of Nuclear Displacements on the Emission Spectrum and Lifetime.- 4.3. Numerical Estimates of Vibronic Effects.- 5. Triplet-Singlet Transitions and Selection Rules.- 5.1. The Mixing of ??* and n?* States.- 6. Relaxation Processes in Molecules.- 6.1. Vibrational Relaxation.- 6.2. Electronic Relaxation.- 6.3. Intersystem Crossing.- 6.4. Spin Polarization.- References.- 2 Experimental Techniques.- A Fluorescence Instrumentation and Methodology.- 1. Basic Considerations.- 1.1. General Description of a Spectrofluorimeter.- 1.2. Representation of Spectra.- 1.3. Calculation of Quantum Yields.- 1.4. Polarization Spectra.- 2. Methodology.- 2.1. Instrument Calibration.- 2.2. Correction for Sample Variations.- 2.3. Cuvettes.- 3. Criteria for a Spectrofluorimeter.- 3.1. Sensitivity.- 3.2. Resolution.- 3.3. Sample Compartment.- 3.4. Photomultipliers.- 3.5. Amplifiers.- 3.6. Summary.- References.- B Direct Measurement of Fluorescence Lifetimes.- 1. Introduction.- 2. Instrumentation.- 2.1. Instrument Considerations.- 2.2. Oscilloscope Techniques.- 2.3. Curve Normalization Techniques.- 2.4. Gated Photomultiplier Detection.- 2.5. Single-Photon Counting.- References.- C Phosphorescence Instrumentation and Techniques.- 1. General Instrumentation.- 1.1. Light Choppers.- 1.2. Photomultipliers.- 1.3. Sample-Cooling Devices.- 2. Matrices.- 3. Population of the Triplet State.- 3.1. Spectra.- 3.2. Quantum Yields.- 3.3. Lifetimes.- 3.4. Polarization of Phosphorescence.- References.- 3 The Excited States of Nucleic Acids.- 1. History and Introduction.- 2. Structures, Nomenclature, and Abbreviations.- 3. Excited States of Monomers.- 3.1. Relevance of Low-Temperature Experiments.- 3.2. Emission Spectra and Other Experimental Parameters.- 3.3. Sensitized Phosphorescence Spectra.- 3.4. Wavefunctions of the Excited States.- 4. Excited States of Oligonucleotides and Polynucleotides at Low Temperature.- 4.1. Types of Interactions.- 4.2. Excited States of Dinucleotides.- 4.3. Excited States of Polynucleotides.- 5. Excited States at Room Temperature.- 5.1. Energy Levels.- 5.2. Nonradiative Rates in Aqueous Solution.- 5.3. Triplet-State Molecules in Aqueous Solution.- 5.4. Temperature Dependence of Fluorescence.- 5.5. Speculations about Fluorescence Quenching and Temperature Effects.- 6. Excited-State Precursors of Photoproducts.- 6.1. Photohydrates.- 6.2. The Cytosine-Thymine Adduct.- 6.3. Photodimers of Pyrimidines.- 6.4. Sensitized Pyrimidine Dimers in Polynucleotides.- 7. Energy Transfer in Polynucleotides.- 7.1. General Considerations.- 7.2. Theory of Energy Transfer.- 7.3. Forster Energy Transfer.- 7.4. Experiments and Calculations.- 8. Transfer RNA.- 8.1. The Role of Odd Bases.- 8.2. tRNAPhe Studies.- References.- 4 Fluorescent Protein Conjugates.- 1. Introduction.- 2. Chemistry of Conjugation.- 2.1. Functional Groups in Proteins and in the Label.- 2.2. Dye Structures.- 3. Experimental Procedures for Labeling.- 3.1. Conditions of Labeling.- 3.2. Isolation of the Labeled Conjugate.- 3.3. Determination of the Degree of Labeling.- 3.4. Fractionation According to the Degree of Labeling.- 4. Effect of the Label on the Properties of the Protein.- 5. Excitation and Emission Spectra.- 5.1. Spectral Data.- 5.2. Changes Due to Alterations in Environment of the Dye Molecule.- 5.3. Electronic Mechanisms Responsible for Changes.- 5.4. Changes Due to Photochemical Reactions.- 6. Lifetime, Decay Time, and Quantum Yield.- 7. Energy Transfer.- 8. Polarization of Fluorescence.- 9. Visible Tracing.- 9.1. Coons Fluorescent Antibody Technique.- 9.2. Quantitative Precipitation Test.- 9.3. N-Terminal Analysis.- 10. Noncovalently Bound Labels.- References.- 5 The Luminescence of the Aromatic Amino Acids.- 1. Introduction.- 2. Excitation of the Aromatic Amino Acids.- 2.1. Excitation by Near-Ultraviolet Radiation: Ultraviolet Absorption Spectra.- 2.2. Excitation by Higher-Energy Radiation.- 3. Environmental Effects upon the Fluorescence of the Aromatic Amino Acids.- 3.1. Temperature.- 3.2. Physical State.- 3.3. Solvent.- 4. Fluorescence Quantum Yields and Lifetimes for the Aromatic Amino Acids.- 5. Fluorescence of Derivatives of the Aromatic Amino Acids.- 5.1. Tryptophan Derivatives.- 5.2. Tyrosine Derivatives.- 5.3. Phenylalanine Derivatives.- 5.4. Oligopeptides Containing Tryptophan and/or Tyrosine.- 6. Radiationless Deactivation of the Excited State.- 7. Phosphorescence of the Aromatic Amino Acids.- 7.1. Temperature Dependence and Solvent Dependence.- 7.2. Tryptophan.- 7.3. Tyrosine.- 7.4. Phenylalanine.- 8. Polarization of Luminescence.- 8.1. Theory.- 8.2. Phenol and Tyrosine.- 8.3. Indole and Tryptophan.- 9. Energy Transfer in Oligopeptides.- 9.1. Radiationless Exchange.- 9.2. Intermolecular Transfer.- 9.3. Intramolecular Transfer in Tyrosine Oligopeptides.- 9.4. Intramolecular Transfer in Oligopeptides Containing Tryptophan and Tyrosine.- 10. Thermoluminescence of the Aromatic Amino Acids.- References.- 6 Luminescence of Polypeptides and Proteins.- 1. Historical Survey.- 1.1. Existence of Excited States.- 1.2. Protein Fluorescence.- 2. Luminescence of Synthetic Polypeptides.- 2.1. Chemistry and Stereochemistry of Polypeptides.- 2.2. Homopolypeptide Luminescence.- 2.3. Heteropolymer Luminescence: Aromatic Amino Acid Systems.- 2.4. Quenching Studies.- 2.5. Photochemistry of Polytyrosine.- 3. Luminescence of Natural Polypeptides: Hormones and Antibiotics.- 3.1. Phenylalanine Systems.- 3.2. Tyrosine-Containing Polypeptides.- 3.3. Tryptophan-Containing Polypeptides.- 3.4. Summary.- 4. Luminescence of Proteins-Class A Proteins.- 4.1. Fluorescence Spectra.- 4.2. Fluorescence Quenching.- 4.3. Phosphorescence.- 4.4. Fluorescence Lifetime.- 4.5. Phosphorescence Lifetime.- 4.6. Temperature-Induced Quenching.- 4.7. Acid Denaturation.- 4.8. Muscle Proteins.- 4.9. Summary.- 5. Luminescence of Proteins-Class B Proteins.- 5.1. Introduction.- 5.2. Tyrosine Fluorescence.- 5.3. Tyrosine Fluorescence and Phosphorescence Spectra.- 5.4. Tyrosine Quantum Yield.- 5.5. Excitation Spectra of Tyrosine.- 5.6. Tyrosine Phosphorescence Yield and Decay Time.- 5.7. Electronic Energy Transfer.- 5.8. Fluorescence Polarization Spectra.- 5.9. Phosphorescence Polarization Studies.- 5.10. Tryptophan Excitation Spectra.- 5.11. Quantum Yields of Tryptophan Residues.- 5.12. Solvent Perturbation.- 5.13. Solvent Isotopic Effect.- 5.14. Temperature Dependence of Quantum Yields.- 5.15. Energy Loss at 77 K.- 5.16. Luminescence Lifetimes.- 5.17. Fluorescence Spectra of Protein Tryptophan Residues.- 5.18. Phosphorescence Spectra of Tryptophan.- 5.19. Stokes' Shift of Fluorescence.- 5.20. Heterogeneity of Environment.- 5.21. Heterogeneity of Phosphorescence.- 5.22. Transfer and Heterogeneity.- References.

243 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented numerical quantum mechanical scattering calculations for the collinear H+H2 reaction on a realistic potential energy surface with an 0.424 eV (9.8 kcal) potential energy barrier.
Abstract: We present numerical quantum mechanical scattering calculations for the collinear H+H2 reaction on a realistic potential energy surface with an 0.424 eV (9.8 kcal) potential energy barrier. The reaction probabilities and rate constants are believed to be accurate to within 2% or better. The calculations are used to test the approximate theories of chemical dynamics. The reaction probabilities for ground vibrational state reagents agree well with the vibrationally adiabatic theory for energies below the lowest threshold for vibrational excitation, except when the reaction probability is less than about 0.1. For these low reaction probabilities no simple one-mathematical dimensional theory gives accurate results. These low reaction probabilities occur at low energy and are important for thermal reactions at low temperatures. Thus, transition state theory is very inaccurate at these low temperatures. However, it is accurate within 40% in the higher temperature range 450–1250°K. The reaction probabilities for hot atom collisions of ground vibrational state reagents with translational energies in the range 0.58 to 0.95 eV agree qualitatively with the predictions of the statistical phase space theory. For vibrationally excited reagents the vibrational adiabatic theory is not accurate as for ground vibrational state reagents. The lowest translational energy of vibrationally excited reagents above which statistical behavior manifests itself is less than 1.0 eV.

221 citations


Journal ArticleDOI
TL;DR: In this article, a normal molecular vibration is strongly excited by a picosecond light pulse and the rise and decay of the excess population of the first excited vibrational state (electronic ground state) is observed with a delayed probe pulse.
Abstract: A normal molecular vibration is strongly excited by a picosecond light pulse. The rise and decay of the excess population of the first excited vibrational state (electronic ground state) is observed with a delayed probe pulse. These measurements give, for the first time, values of the lifetimes of molecular vibrations in liquids.

221 citations



Journal ArticleDOI
TL;DR: In this paper, the 2p-3h character of negative-parity states of 15 N was studied using the two-particle transfer 13 C( 3 He, p) 15 N reaction.

Journal ArticleDOI
TL;DR: In this paper, a general scheme for calculating relative nonradiative decay rates of initially selected vibronic levels in polyatomic molecules is developed, and the contribution of vibrational contribution is calculated approximately in the large molecule (statistical) limit by deriving the appropriate (modified) energy gap law.
Abstract: A general scheme for calculating relative nonradiative decay rates of initially selected vibronic levels in polyatomic molecules is developed. Here we are concerned only with relative rates corresponding to initial vibronic states in some particular electronic manifold decaying into some other particular electronic manifold. Therefore we need only consider the exact density‐of‐states‐weighted‐Franck—Condon factor accounting for the vibrational contribution to the over‐all nonradiative decay rate. This contribution is calculated approximately in the large molecule (statistical) limit by deriving the appropriate (modified) energy gap law. The contributions of ``special'' modes (e.g., optically excited modes, and modes with large geometry and/or frequency shifts) are partitioned from those of the other modes by techniques similar to ones developed earlier to treat cis—trans isomerism and are calculated explicitly. Excellent agreement with the recent low pressure experimental results of Spears, Abramson, and Rice for the S1→ T1 intersystem crossing rates from individual vibronic states in benzene and perdeuterobenzene is obtained, but only by taking proper account of the effects of geometry and frequency changes of the various vibrational modes involved in the transition. The sharp dependence of the relative nonradiative rates for a progression in an optical mode upon the frequency shift in that mode leads to the possibility of evaluating the vibrational frequencies in an electronic state by measuring the radiationless decay rate into that electronic state (e.g., in the benzene case determining T1 vibrational frequencies from S1→ T1 decay rates). Finally, we comment upon recent low pressure experimental results for β‐naphthylamine, monofluorobenzene, and upon some observed temperature dependences of radiationless transition rates in matrices.

Journal ArticleDOI
TL;DR: Many but not all bands of the 2600 A absorption system of benzene involving vibrational levels more than 3000 cm−1 above the zero point level of the excited state are seen to be more or less diffuse when photographed under very high resolution.

Journal ArticleDOI
TL;DR: In this paper, it was found that with the laser excitation, narrow lines (≈1 cm-1) appeared instead of broad bands ( ≥200 cm- 1) in the fluorescence spectrum of both the crystalline and glass-like solid solutions.

Journal ArticleDOI
TL;DR: In this paper, a strong resonance Raman effect of the I−3 ion when excited by the ultraviolet lines at 3638 and 3511 A of an argon ion laser, high intensity overtone progressions of the symmetric vibration νi were observed.

Journal ArticleDOI
TL;DR: In this article, a reasonably complete set of phenomenological discrete and ionization cross sections for argon is given using combinations of data and theoretically meaningful extrapolations of the generalized oscillator strengths.
Abstract: A reasonably complete set of phenomenological discrete and ionization cross sections for argon is given using combinations of data and theoretically meaningful extrapolations of the generalized oscillator strengths. After including estimates of inner‐shell cross sections, the degradation of electrons in Ar is considered. Calculations of the final populations for each excited state are given as a function of incident energy and when applied to ionization, results in electron volts per ion pair values near 29 eV. Inner shells in our work appear to contribute by adding on the order of 5% to the loss function at energies above a kilovolt.

Journal ArticleDOI
TL;DR: In this paper, Trajectory calculations were made using various types of modified London-Eyring-Polanyi-Sato (LEPS) surfaces to obtain the vibrational energy level distributions for comparison with experimental results.
Abstract: The reaction of atomic hydrogen with molecular fluorine produces vibrationally excited hydrogen fluoride with v′ ⩽ 8>. Maximum population is achieved in v′ = 6. It is estimated that 58 per cent of the available energy of reaction is initially present as HF v′→0 †. Trajectory calculations have been made using various types of modified London-Eyring-Polanyi-Sato (LEPS) surfaces to obtain the vibrational energy level distributions for comparison with experimental results. A general conclusion is that in all cases, the predicted distribution is too narrow. No one surface could simultaneously give an entirely satisfactory prediction of the product vibrational energy distribution, activation energy with related rate constant and reaction enthalpy. It is concluded that a systematic method of selection of the value for De 3 for the first 3Σ state will be necessary if a surface is to be transferred between related reactions. A ‘best’ surface is selected and shown to be compatible with the known activation energy a...

Journal ArticleDOI
TL;DR: In this article, a set of 40 molecular constants capable of reproducing a total of ∼1200 vibrational-rotational energy levels with a standard deviation of 0.006 cm−1 is tabulated.

Journal ArticleDOI
TL;DR: In this paper, it is confirmed that absorption proceeds at a rate proportional to the second-order product of the complex field amplitude, whether the light field is homogeneous or evanescent, and that the emission process follows a reciprocity principle.
Abstract: Experiments have been carried out to investigate the excitation of molecules by evanescent light, and the emission of evanescent light in the fluorescence of excited molecules. It is confirmed that the absorption proceeds at a rate proportional to the second-order (normally ordered) product of the complex field amplitude, whether the light field is homogeneous or evanescent, and that the emission process follows a reciprocity principle.

Journal ArticleDOI
TL;DR: In this article, the effects of geometrical restrictions on the intramolecular CT (charge transfer) interactions in the excited state have been investigated for the (anthryl)-(CH 2 ) n -( p -N, N-dimethylaminophenyl) systems (n = 0, 1, 2, 3).

Journal ArticleDOI
TL;DR: In this paper, the VUV emission characteristics of Xenon for pressures from 15 to 450 psi were presented, with and without mirrors, and the mean radiative lifetime was 2×10−8.
Abstract: Vacuum ultraviolet (VUV) emission characteristics of xenon for pressures from 15 to 450 psi are presented. Stimulated emission was observed above 200 psi. Experiments were run both with and without mirrors. Without mirrors, the emission was 150 A wide centered at 1700 A, and the mean radiative lifetime was 2×10−8. The energy conversion efficiency was ∼ 20%. With mirrors above 200 psi the emission width narrowed to 17 A centered at 1716 A, and the output was highly directional. The pulse width narrowed from 50 to ∼ 3 nsec.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of an experimental study of electronic energy transfer in gaseous mixtures excited by a pulsed electric discharge, and the relative contributions of two energy transfer mechanisms involving atom-atom and molecule-atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure.
Abstract: In this paper we present the results of an experimental study of electronic energy transfer in xenon‐argon, krypton‐argon, and xenon‐krypton gaseous mixtures excited by a pulsed electric discharge. Spectroscopic evidence for electronic energy transfer is based on the decrease in the intensity of the vacuum ultraviolet emission of the excited diatomic homonuclear rare gas molecules in the presence of small amounts (10–1000 ppm) of a foreign rare gas atom, while the visible emission spectrum of the host gas is parctically unmodified under these conditions. The relative contributions of two energy transfer mechanisms involving atom‐atom and molecule‐atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure. We have determined the cross sections for energy transfer from the lowest metastable Ar and Kr excited states, and from the lowest excited state of Ar2* and Kr2* to ground state Xe, and from metastable excited Ar and from Ar2* to ground state Kr. The molecule‐atom energy transfer process is characterized by large ∼ 10−14 cm2 cross sections. A simplified theoretical treatment of excited molecule‐ground state atom collisions provides a proper rationalization of these large cross sections in terms of long range dipole‐dipole coupling.

Journal ArticleDOI
TL;DR: In this paper, a practical method for computing the T-matrix elements for a rotating, vibrating oscillator is presented. But the method is not suitable for the case of rotational transitions from the ground to the first accessible excited rotational state.
Abstract: A practical method is presented for computing the T‐matrix elements for a rotating, vibrating oscillator. A simple model is used which approximates the features of the He–H2 system. It is found that the rigidrotor approximation is in error even at energies well below the threshold for vibrational excitation. For computation of rotational transitions from the ground to the first accessible excited rotational state, many of the excited rotational transitions may be neglected but some of the excited vibrational transitions must be included. At high energies, it is shown that for any particular transition many of the states not strongly coupled to the states involved in the transition may be neglected. It is found that the computation of T‐matrix elements for vibrational transitions in the presence of rotational transitions is not prohibitively time consuming. In computing the total cross section, it is shown that a calculation including only the ground state gives remarkably good results.

Journal ArticleDOI
TL;DR: In this article, the LCAO-MO-SCF Pariser-Parr-Pople method was used to estimate the ππ* triplet states energies with the use of large configuration interactions.
Abstract: Complete triplet—triplet absorption spectra (2000–10000 A) were measured in alcoholic solution at 113°K with naphthalene, anthracene, tetracene, and a few methylated derivatives. Several new bands were observed. Calculations of the higher ππ* triplet states energies with the LCAO—MO—SCF Pariser—Parr—Pople method were improved by the use of large configuration interactions. These include many doubly excited configurations with respect to both the ground singlet state S0 and the lowest triplet state T1, thanks to the systematic use of all monoexcitations with respect to S0 plus all monoexcitations with respect to T1. The comparison of all experimental and theoretical results for the three polyacenes allows one to modify a few previous assignments and to give a general tentative assignment for all observed transitions.

Journal ArticleDOI
TL;DR: In this article, an extended Hartree-Fock method for excited states is proposed, starting from the ground state Hartree Fock molecular orbitals and allowing mixing within occupied and vacant subspaces, respectively, to minimize the energy of a single configuration excited state.

Journal ArticleDOI
TL;DR: In this paper, rate equations were developed and used to calculate the monochromatic laser power densities that are required to effectively saturate the excited atom population in typical hot gases.

Journal ArticleDOI
TL;DR: In this paper, the theory of photoionization measurements for a general atomic system is developed in terms of a density matrix which determines the ejected electron and residual ion polarizations as a function of the target atom and incident photon polarization states.
Abstract: The theory of photoionization measurements for a general atomic system is developed in terms of a density matrix which determines the ejected electron and residual ion polarizations as a function of the target atom and incident photon polarization states. Expressions are derived which relate the photoelectron angular distribution and spin polarization parameters to the reduced matrix elements for the photoelectric transition. These expressions incorporate the fine structure of the atomic levels and the complete interaction between the residual ion and the ejected electron. The polarization of the residual ions which are formed in excited states is treated in terms of the subsequently emitted decay radiation.

Journal ArticleDOI
TL;DR: In this paper, the core level electron spectra of CO 2, CS 2 and COS excited by Mg Kα radiation have been studied to identify shake-up satellite lines associated with ionization from these levels.

Journal ArticleDOI
TL;DR: In this article, an exact calculation of the ground state and the first excited state withm = 0 and even parity of a hydrogenic system in a magnetic field is described, and results are given for the energy and the main features of the wave functions.
Abstract: An exact calculation of the ground state and of the first excited state withm = 0 and even parity of a hydrogenic system in a magnetic field is described, and results are given for the energy and the main features of the wave functions. Tor the excited state the shape of the nodal surface is given, and it is shown that in this case no contradiction exists between the noncrossing rule and the nodal-surface criterion for the connection of the levels in the low- and high-field regions.