Showing papers in "Chemical Physics Letters in 1973"
TL;DR: In this paper, the existence of two excited species differing in polarity and in the orientation of the N(CH 3 ) 2 group has been attributed to the presence of an excimer.
Abstract: Two fluorescense bands of p -N,N-dimethylamino-benzonitrile (DAB, I) have previously been ascribed to two emitting states, the strongly polar 1 L b and the less polar 1 L b , or to the presence of an excimer. However, the parallel polarization of both emission bands in derivatives II and III, the effect of substituents, especially the steric effect on the dimethylamino group, and the lack of concentration effects in a broad concentration range, invalidate these hypotheses. We tentatively assign the emissions to the existence of two excited species differing in polarity and in the orientation of the —N(CH 3 ) 2 group: a lone pair perpendicular or parallel to the plane of benzene ring; in the latter case π * y orbitals of the —CN group seem to be involved in the excitation.
701 citations
TL;DR: In this paper, it was shown that N( 4 S) and O( 3 P) atom quenching effects upon chemiluminescence from NO(B 2 π) (θ = 0) are of importance when this emissio values of k 2 = (1.74 ± 0.13) × 10 9 and (4.05 ± 1.17) ×10 9 and 2 mole -2 sec -1 are found at 298 and 196°K respectiv
Abstract: It is shown that N( 4 S) and O( 3 P) atom quenching effects upon chemiluminescence from NO(B 2 π) (θ = 0) are of importance when this emissio Values of k 2 = (1.74 ± 0.13) × 10 9 and (4.05 ± 0.17) × 10 9 & 2 mole -2 sec -1 are found at 298 and 196°K respectiv
204 citations
TL;DR: In this article, a new simple function which is capable of representing the intermolecular pair potential energy of the inert gases is proposed, based on the traditional n -6 reciprocal power potential with the modification that n is regarded as a function of separation rather than as a constant.
Abstract: A new simple function which is capable of representing the intermolecular pair potential energy of the inert gases is proposed. It is based on the traditional n -6 reciprocal power potential with the modification that n is regarded as a function of separation rather than as a constant.
146 citations
TL;DR: The use of overlapping spheres in the SCF Xα scattered-wave method is discussed in this article, which leads to an improved description of both ionization potentials and total energies of molecules where a substantial fraction of the charge due to the valence electrons is distributed over the interatomic region of constant potential.
Abstract: The use of overlapping spheres in the SCF Xα scattered-wave method is discussed. It leads to an improved description of both the ionization potentials and total energies of molecules where a substantial fraction of the charge due to the valence electrons is distributed over the interatomic region of constant potential. The effects of using improved exchange parameters for hydrogen-containing molecules are also considered. Results for ethylene, benzene, and carbon monoxide are reported.
141 citations
TL;DR: In this paper, a perturbation treatment was applied to the nitrogen molecule to predict the vertical ionization potentials of the two lowest ionizations, and it turns out that it is necessary to use a very elaborate form of perturbations in the case of N 2.
Abstract: The nitrogen molecule is one of the simplest and best known examples where Koopmans' theorem not only fails in predicting accurate values for the vertical ionization potentials but even yields the wrong sequence of the two lowest ionizations. In this paper a perturbation treatment we had presented recently is applied to this problem. It turns out that it is necessary to use a very elaborate form of perturbation theory in the case of N 2 .
139 citations
TL;DR: In this article, the authors consider the problem of interpreting quenching kinetics in small molecules (e.g., CN, CH 2, NO 2 and SO 2 ) and argue the importance of analyzing these data in terms of collisional transitions between perturbed (mixed electronic parentage) as opposed to pure (non-spectroscopic) vibronic states.
Abstract: We consider the problem of interpreting quenching kinetics in small molecules [e.g., CN, CH 2 , NO 2 and SO 2 ] which show significant intrinsic interactions, and argue the importance of analyzing these data in terms of collisional transitions between perturbed (mixed electronic parentage) as opposed to pure (non-spectroscopic) vibronic states. Time resolved experiments are discussed which could determine more unambiguous deactivation cross sections and spectral assignments.
131 citations
TL;DR: In this article, a method for eliminating the off-diagonal lagrangian multipliers which appear in open-shell SCF theory is given, which leads to a set of coupled eigenvalue equations which can be easily solved for a new guess to the SCF orbitals.
Abstract: A method is given for eliminating the off-diagonal lagrangian multipliers which appear in open-shell SCF theory. This leads to a set of coupled eigenvalue equations which is easily solved for a new guess to the SCF orbitals. This procedure has proven more conveient than many others now in use.
126 citations
TL;DR: In this article, the authors describe the generation of a continuum which has a time duration equal to or less than the picosecond pulse which generates it, and the spectrum of the continuum is several thousand wavenumbers in width.
Abstract: This paper describes the generation of a continuum which has a time duration equal to or less than the picosecond pulse which generates it. The spectrum of the continuum is several thousand wavenumbers in width. Experimental methods are presented which enable one for the first time to conduct absorption spectroscopy measurements in the picosecond scale. As an example of this method we describe the absorption and emission picosecond kinetics of a bleachable dye 3,3 diethyloxodicarbocyanine (DODC).
119 citations
TL;DR: Onsager's theory of dipole moments is modified for radially inhomogeneous permittivity [form ϵ( r )=ϵ B exp(κ/ r )] arising at the cavit as mentioned in this paper.
Abstract: Onsager's theory of dipole moments is modified for radially inhomogeneous permittivity [form ϵ( r )=ϵ B exp(—κ/ r )] arising at the cavit Calculations show more consistent agreement between gaseous and liquid dipole moments with the modified theory.
114 citations
TL;DR: In this article, Monte Carlo free energy results for a fluid of point dipoles embedded in hard spheres are reported for a multistage sampling method compared with thermodynamic integration techniques, and the resulting free energies are compared with recent theoretical results obtained from the mean spherical model approximation and from a perturbation theory approach.
Abstract: This reports some Monte Carlo free energy results for a fluid of point dipoles embedded in hard spheres. The multistage sampling method is compared with thermodynamic integration techniques. The resulting free energies are also compared with recent theoretical results obtained from the mean spherical model approximation and from a perturbation theory approach.
111 citations
TL;DR: In this article, the reaction mechanisms of molecular systems in the ground singlet state are discriminated with the triplet stability-instability criterion of restricted Hartree-Fock (RHF) solution for the entire system and with the phase continuity criterion of the highest occupied orbital involved.
Abstract: The reaction mechanisms of molecular systems in the ground singlet state are discriminated with the triplet stability—instability criterion of the restricted Hartree—Fock (RHF) solution for the entire system and with the phase continuity criterion of the highest occupied orbital involved. The criteria used are discussed in relation to the outcomes from the configuration-interaction approach.
TL;DR: The use of recently available frequency, 13C frequency shift, Coriolis coupling, and centrifugal distortion data enables the GHFF of formaldehyde to be determined with some degree of precision as discussed by the authors.
Abstract: The use of recently available frequency, 13C frequency shift, Coriolis coupling, and centrifugal distortion data enables the GHFF of formaldehyde to be determined with some degree of precision. Excellent agreement is obtained between the experimentally determined interaction force constants and those predicted by the most recent ab initio calculations of Meyer and Pulay.
TL;DR: In this paper, the nuclear magnetic resonance lineshape of the protons in the amphiphile alkyl chains in lamellar liquid crystals is calculated and it is found that the inclusion of intra molecular dipolar interactions not averaged to zero explains the shape of the experimentally observed spectrum.
Abstract: The nuclear magnetic resonance lineshape of the protons in the amphiphile alkyl chains in lamellar liquid crystals is calculated. It is found that the inclusion of intra molecular dipolar interactions not averaged to zero explains the shape of the experimentally observed spectrum.
TL;DR: In this paper, a perturbation theory analysis of the Δ E SCF ionization energies produces a second order correction to the Koopmans' theorem values which is mimicked directly by use of a transition Fock operator.
Abstract: A perturbation theory analysis of the Δ E SCF ionization energies produces a second order correction to the Koopmans' theorem values which is mimicked directly by use of a “transition Fock operator”. This is shown numerically by some opposite atomic calculations. The relation to Slater's “transition state” is discussed, and advantages are pointed out.
TL;DR: In this paper, the X-ray photoelectron spectroscopy (ESCA) has been used in a study of CO and O2 chemisorbed on polycrystalline tungsten sample.
Abstract: X-ray photoelectron spectroscopy (ESCA) has been used in a study of CO and O2 chemisorbed on a polycrystalline tungsten sample. Working under ultra-high vacuum conditions, the surface was cleaned and then covered with known monolayer and fractional monolayer quantities of adsorbed CO and O2. The O(ls) and C(ls) spectral features were detected, and the influence of an adsorbed layer on the tungsten spectral features was determined. A chemical shift of 3.4 eV in the O(ls) line from chemisorbed CO is related to the different modes of bonding of CO to tungsten. A model calculation of the photoelectron yields expected from an adsorbed monolayer is in good agreement with the experimental results.
TL;DR: The deuteron resonance of five of the eleven methylene and methyl groups of the paraffinic chains is distinctly resolved in this article, and the orientation of the monocrystalline lamellar mesophare is varied with respect to the external magnetic field.
Abstract: The deuteron resonance of five of the eleven methylene and methyl groups of the paraffinic chains are distinctly resolved. The orientation of the monocrystalline lamellar mesophare is varied with respect to the external magnetic field. The evolution f the resonance positions with orientation confirms that the system has local uniaxial symmetry on time scale longer than a few 10 −6 sec.
TL;DR: In this article, the effective transition frequencies and oscillator strenghts obtained from principal representations of spectral moments, or from variational procedures using appropriate square-integrable basis functions, are employed in the Stieltjes imaging of atomic and molecular photoabsorption profiles.
Abstract: The effective transition frequencies and oscillator strenghts obtained from principal representations of spectral moments, or from variational procedures using appropriate square-integrable basis functions, are employed in the Stieltjes imaging of atomic and molecular photoabsorption profiles.
TL;DR: The vibrational structure of the 2B1 ← 2A1 system of NO2 has been assigned to a progression in ν′2. as mentioned in this paper showed that the bending potential function is expressed as a rapidly converging Taylor series expansion about the linear configuration.
Abstract: The vibrational structure of the 2B1 ← 2A1 system of NO2 has been assigned to a progression in ν′2. Vibrational analyses for three isotopic species have been made using a hamiltonian which allows explicitly for a large-amplitude bending vibration. The system origin for the normal isotopic species has been assigned an extrapolated value of 14743.5 cm−1. The bending potential function is expressed as a rapidly converging Taylor series expansion about the linear configuration. There is no evidence that the equilibrium configuration is nonlinear.
TL;DR: In this paper, the eigenstates of a new set of approximate constants of the motion of two-electron atoms are very nearly those obtained by diagnolizing 1/r ij within a complex.
Abstract: the eigenstates of a new set of approximate constants of the motion of two-electron atoms are very nearly those obtained by diagnolizing 1/ r ij within a complex. They easily obtained by reducing SO(4) × SO(4) to SO(4) in a novel way.
TL;DR: In this paper, a UHV instrument was used to obtain the ECA spectra for a film of aluminium which was evaporated in situ and subsequently oxidised in stages, and both bulk and surface plasmon losses for Al were observed on the clean film and chemical shifts in 2s and 2p lines were determined after oxidation.
Abstract: ESCA spectra have been obtained on a UHV instrument for a film of aluminium which was evaporated in situ and subsequently oxidised in stages. Both bulk and surface plasmon losses for Al were observed on the clean film and chemical shifts in the 2s and 2p lines were determined after oxidation.
TL;DR: In this paper, Hartree-Fock calculations were performed on the lowest five (singlet and triplet) Rydberg states and the 2 Π g state of the positive ion.
Abstract: Extensive configuration interaction calculations (1000 to 1500 determinants) have been carried out for the six low-lying valence states of carbon dioxide in order to provide reliable assignments for the transitions to these states. In addition, Hartree—Fock calculations were performed on the lowest five (singlet and triplet) Rydberg states and the 2 Π g state of the positive ion. These results yield an accurate description of the excited states of carbon dioxide and provide for definitive assignments of the transitions observed by optical and electron impact studies (for the five states known experimentally, the calculations agree to within 0.2 eV of the experimental transition energies).
TL;DR: In this paper, the authors used a narrow band, pulsed dye laser in the region between 5934 and 5940 A to obtain a partial rotational analysis of a K = 0 subband of a 2 B 2 ← 2 A 1 transition.
Abstract: By exciting NO 2 with a narrow band, pulsed, dye laser in the region between 5934 and 5940 A, we have obtained a partial rotational analysis of a K = 0 sub-band of a 2 B 2 ← 2 A 1 transition. In addition, we find evidence for a 2 B 1 ← 2 A 1 transition in this region. By measuring the decay of resolved fluorescence features, we have determined the lifetimes of these two states, and find that they are markedly different.
TL;DR: The zero-field splitting of the non-phosphorescent lowest triplet state of free base porphin is measured by observing microwave induced changes in the fluorescence of this molecule as a guest in a Shpolskii-matrix of n -octane at 4.2°K.
Abstract: The zero-field splitting of the non-phosphorescent lowest triplet state of free base porphin is measured by observing microwave induced changes in the fluorescence of this molecule as a guest in a Shpolskii-matrix of n -octane at 4.2°K. The doublet character of the fluorescence spectrum of the system also manifests itself in the microwave spectrum. It is proved that this doublet structure is caused by two physically distinct free base porphin molecules in the host lattice.
TL;DR: In this article, a recent theory for intermolecular interactions is modified by the exclusion of a self-exchange contribution and the inclusion of dispersive inter-interactions.
Abstract: A recent theory for intermolecular interactions is modified by the exclusion of a “self-exchange” contribution and the inclusion of dispersive inte
TL;DR: In this article, an independent-electron -pair approximation (including intra-and inter-pair correlation effects) was performed for the ground state of acetylene, ethylene and their protonated cations.
Abstract: Calculations based on the independent-electron -pair approximation (including intra- and inter-pair correlation effects) were performed for the ground state of acetylene, ethylene and their protonated cations. The classical and non-classical (bridged) structures were considered for the cations. The results of the calculations indicate that the bridged forms are lower in energy by about 7 kcal/mole and 9 kcal/mole for C2H+3 and C2H+5, respectively. This is mainly due to the larger correlation energy for the non-classical forms. On Hartree-Fock level (including polarization functions) the classical and non-classical structures of C2H+5 have practically the same energy. For C2H+3 the inclusion of correlation effects reverses the relative stability of the two structures.
TL;DR: In this paper, the photoelectron spectrum of HCP has been obtained, ionization potentials are found at 10.79 ± 0.01 eV (X 2 Π) and 12.86 ± ε (A 2 Σ).
Abstract: The photoelectron spectrum of HCP has been obtained, Ionization potentials are found at 10.79 ± 0.01 eV (X 2 Π) and 12.86 ± 0.01 eV (A 2 Σ). By comparison with HCP, a new interpretation of the first photoelectron band of HCN has been proposed which involves a Renner-Teller interaction in the Σ + vibronic states of the molecular ion.
TL;DR: In this paper, a discontinuity in 13 C-isotope shifts was used to fix the location of a diffuse 00 of gaseous 12 C 2 H 2 at 54 116 cm −1.
Abstract: A discontinuity in 13 C-isotope shifts is used to fix the location of a diffuse 00 of gaseous 12 C 2 H 2 at 54 116 cm −1 . The shifts and analogy with a known band system of HCN suggest the assignment B 1 B u - X 1 Σ + g for the new electronic transition.
TL;DR: In this paper, a technique for the computer simulation of the motion of 10,000 simulated molecules is described, where the number of computer operations per time-step is proportional to the number simulated particles even though the force of interaction may be long range and no force cut-off is employed.
Abstract: A technique is described for the computer simulation of the motion of 10000 simulated molecules. The number of computer operations per time-step is proportional to the number of simulated particles even though the force of interaction may be long range and no force cut-off is employed.
TL;DR: The PCILO method accounts correctly for the preferred conformation of glyoxal, butadiene, benzaldehyde, benzoic acid, biphenyl and 2,2′-difluorobiphenyl as discussed by the authors.
Abstract: Contrary to the CNDO/2 method, the PCILO method accounts correctly for the preferred conformation of glyoxal, butadiene, benzaldehyde, benzoic acid, biphenyl and 2,2′-difluorobiphenyl.
TL;DR: In this paper, an analytic formulation for the total potential in atomic and molecular systems, based on the electrostatic approach from the Hellmann-Feynman theorem, is given.
Abstract: An analytic formulation is given for the total potential in atomic and molecular systems, based on the electrostatic approach from the Hellmann-Feynman theorem. The potential function is obtained from the analytic solution of the Poisson equation using charge densities expressed as a superposition of gaussian functions. The method is independent of the specific LCAO approximation used for the calculation of the charge distribution function. The calculation of the potential and its derivatives to a rapid algorithm form, which can be used for the evaluation of various electronic properties and the treatment of experimental situation, even for large molecular systems.