Showing papers on "Absorption spectroscopy published in 1976"

Doppler-Free Laser Polarization Spectroscopy

Abstract: We have demonstrated a sensitive new method of Doppler-free spectroscopy, monitoring the nonlinear interaction of two monochromatic laser beams in an absorbing gas via changes in light polarization. The signal-to-background ratio can greatly surpass that of saturated absorption. Polarization spectra of the hydrogen Balmer-$\ensuremath{\beta}$ line, recorded with a cw dye laser, reveal the Stark splitting of single fine-structure components in a Wood discharge.

Observations and interpretation of x-ray absorption edges in iron compounds and proteins.

Abstract: X-ray absorption spectra near the Kalpha edge have been measured in various iron group compounds using the intense synchrotron radiation at the Stanford Synchrotron Research Project. In the cubic compounds KMF3 where M = Mn+2, Fe+2, Co+2, Ni+2, and Zn+2, well resolved lines were observed and assigned to the 1s leads to 3d, 1s leads to 4s, and 1s leads to 4p transitions. The observed energies agreed rather well with the spectroscopic energy levels of the Z + 1 ion and the intensities are shown to agree with those expected on the basis of one electron transitions of the form Z 1s2dn(L,S) leads to (Z + 1)1s2dnn'l'(L",S). The energies of the intense 1s leads to 4p transition increase by about 5 V going from KFeF3 to K2NaFeF6, but only by about 1 V from K4Fe(CN)6 to K3Fe(CN)6. The transitions confirm that upon oxidation of the hexacyanides the iron electronic structure barely changes. In the iron sulfur protein rubredoxin, where the iron is bound to a tetrahedron of sulfurs, the 1s leads to 3d transition was about seven times more intense than the same transition in an octahedrally coordinated compound. These intensities parallel those observed in the d-d transitions of optical spectra, because in both types of spectra the intensities depend upon 4p admixture. In the heme protein cytochrome c, upon oxidation the 1s leads to 4p transition shifts only about 1 V to higher energies similar to the iron hexacyanides. These results are discussed in terms of covalent bonding.

C–H vibrational states of benzene, naphthalene, and anthracene in the visible region by thermal lensing spectroscopy and the local mode model

Abstract: Visible (red) absorption spectra of benzene (h6 and d6), methyl substituted benzenes, naphthalene, and anthracene are presented as seen by thermal lensing spectroscopy. It is shown how this highly sensitive laser‐based technique can easily detect transitions having absorption coefficients as small as 10−6 cm−1. The observed transitions are principally due to C–H stretching vibrations at the sixth quantum of excitation. The local mode (LM) model for describing such molecular states is explored in some detail with reference to the C–H excitations in benzene. Based on a two parameter empirical fit, the LM model can give a true C–H stretch ’’mechanical’’ frequency; it successfully predicts isotope effects; and it fully determines the energy level scheme at any quantum of excitation. The LM energy level scheme for the 462 C–H stretching states at the sixth quantum of excitation is presented. A majority of these states are only mildly anharmonic; one state in fact is a perfect harmonic of the fundamental. However, only the most anharmonic state of the 462 is the spectroscopically allowed one. The LM model, already introduced in the literature, is seen to be an excellent zeroth order description of those very same highly excited vibrational states most readily accessible to a sensitive absorption technique such as that offered by the thermal lensing effect.

2.3. Absorption and Emission by Atmospheric Gases

Abstract: Publisher Summary This chapter focuses on absorption and emission by atmospheric gases. At centimeter and shorter wavelengths, absorption and emission by atmospheric gases can significantly affect the propagation of electromagnetic radiation through the atmosphere. At frequencies from 1 to 300 GHz, referred to as “microwave frequencies,” absorption by atmospheric gases is dominated by water vapor lines at 22 and 183 GHz, oxygen lines near 60 GHz and at 118 GHz, and relatively narrow and weaker ozone lines above 100 GHz. Non-resonant absorption by water vapor and oxygen has significant effects in the window regions away from the dominant lines. The radiative transfer expressions appropriate for calculating absorption and emission by atmospheric gases are formulated. The general expressions for the spectral-line absorption coefficient are provided, followed by specific expressions for calculating absorption by water vapor and oxygen. Problems associated with the calculation of absorption by these two molecules are discussed. The absorption by microwave lines of ozone and other minor constituents is considered. Finally, the results of calculations of atmospheric absorption and emission, as well as the measured values are presented in the chapter.

Higher ro-vibrational levels of H2O deduced from high resolution oxygen-hydrogen flame spectra between 6200 and 9100 cm-1

Abstract: The spectra of hydrogen-oxygen and acetylene-oxygen flames have been recorded on a Fourier transform spectrometer in the region 6200–9100 cm-1 with a resolution of 0·015 cm-1. In this region, we have performed a detailed analysis of the 2v 2 + v 3, v 1 + v 3, v 1 + v 2 + v 3 - v 2 and v 1 + v 2 + v 3 bands. A primary motive for this study was to obtain higher rotational energy levels for the (021), (101) and (111) vibrational states. Moreover an extensive set of rotational levels of the (010) vibrational state has been deduced from the combined study of hot bands involving the (011), (021) and (111) vibrational states. A room-temperature absorption spectrum of water recorded on a Fourier transform spectrometer in the region 1750–2300 cm-1 (resolution 0·005 cm-1) has also been used to confirm the analysis.

Thermal lens technique: a new method of absorption spectroscopy.

Abstract: Both a single beam and a dual beam (with synchronous detection) thermal lens technique have been employed in the measurement of "colorless" organic compounds in the range 15,700 to 17,400 cm-1 Combination overtones of C-H stretching vibrations in benzene have been identified and agree with previous results obtained by conventional spectroscopy with a long optical path Extinction coefficients as low as 1 X 10(-6) liter mole-1 cm-1 have been accurately determined The sensitivity of the technique has been further demonstrated by measuring the So leads to T1 absorption of anthracene; the spectrum compares favorably with results obtained by conventional techniques

The spectrum and ground state potential curve of Ar2

Abstract: The absorption spectrum of Ar2 has been photographed at a dispersion sufficiently high to allow a rotational analysis of one band system. From the analysis, the vibrational and rotational constants of the five lowest vibrational levels of the ground state have been determined. These spectroscopic data, together with information from long‐range forces and from the second virial coefficient, have been used to calculate the potential curve of the ground state. This calculated curve is compared with other curves which have been proposed.

Some optical properties of the AlxGa1−xAs alloys system

Abstract: Optical transmission data covering the Γ15V–Γ1C absorption edge are presented, together with photoluminescence (PL) results, for AlxGa1−xAs crystals of high purity [n (293 K) <1017 cm−3] for 0

The electronic structure of the uranyl ion: Part I. The electronic spectrum of Cs2UO2Cl4

Abstract: The low-temperature single-crystal optical absorption spectrum of Cs2UO2Cl4 is reported in six different polarizations Measurements have also been made on the 18O compound Zeeman-effect measureme

The electronic structure of NO2. II. The ? 2B2← ? 2A1 and ? 2B1←? 2A1 absorption systems

Abstract: The results of an accurate ab initio study of the electronic structure of NO2 have been applied to an analysis of the two important visible and near infrared absorption systems of this molecule. The long wavelength absorption (λ≳6000 A) arises from an ? 2B2←? 2A1 transition. A theoretical absorption spectrum that is generated from the C2V ab initio potential surfaces of these two states qualitatively reproduces most of the features of an experimental low resolution absorption spectrum between 9000 and 6000 A. The (0–0) band of the transition is predicted to be several times less intense than nearby hot bands even at temperatures as low as 300 K. The computed ? 2B2 spectroscopic parameters are Te=1.18 eV, Re=1.26 A, ϑe=102°, ω1=1461 cm−1, ω2=739 cm−1, and μ=0.46 D. There is a marked difference between experimentally determined ? 2B2 rotational constants and those deduced from the ab initio equilibrium geometry; this datum adds to the rapidly increasing evidence for strong vibronic coupling of the ? 2B2 sta...

Picosecond Flash Spectroscopy of Solvent-Induced Intramolecular Electron Transfer in the Excited 9,9′-Bianthryl

Abstract: Sn←S1 absorption spectra of 9,9′-bianthryl in the visible and near infrared regions have been measured by means of picosecond flash spectroscopy. The Sn←S1 spectra in hexane measured at 500 ps after the exciting pulse were similar to those of anthracene while those in acetone were similar to the superposition of spectra of anthracene anion and cation. The results of the Sn←S1 spectral measurements together with those of the solvent effects upon the fluorescence yield and lifetime indicate an intramolecular electron transfer induced by the interaction with polar solvents in the excited state of 9,9′-bianthryl.

Homogeneous Broadening of Optical Transitions in Organic Mixed Crystals

Abstract: We have used the phenomenon of laser-induced molecular photodissociation to determine the homogeneous linewidth at 2 K of the origin (zero-phonon line) and a vibronic transition in the mixed-crystal absorption spectrum of dimethyl s-tetrazine in durene. From the measured 55-MHz (upper limit) homogeneous width of the origin we conclude that in the vibrationless excited state coherence persists at least during the 6-nsec lifetime. The 29-GHz homogeneous vibronic linewidth is ascribed to vibrational relaxation.

Infrared determination of the orientation of molecules in stearamide monolayers

Abstract: The orientation of molecules in the monomolecular stearamide monolayers has been studied by infrared linear dichroism. By comparing the transmission absorption spectra carried out at different angles of incidence with the reflection absorption spectra obtained by depositing the monolayers on a metal substrate, the orientation of the dipole transition moments for a great number of normal vibration modes of the molecules may be determined to within a few degrees accuracy. Given certain assumptions, the orientation of the molecules themselves can then be deduced.

High resolution absorption spectrum of nitric oxide (NO) in the region of the first ionization limit

Abstract: The absorption spectrum of cold NO gas has been photographed at high resolution between 1400 and 1250 A for two isotopic species. Resolved bands of the Rydberg series converging to vibrational levels of the 1Σ+ ground state of NO+ are studied. They include nf–X bands up to n = 15 and ns–X bands up to n = 11, all of which show sharp rotational structure. The higher members of the np–X series are generally very diffuse with only npσ being sufficiently sharp to show broadened rotational lines. Also mostly diffuse are the ndδ–X bands. The bands ndσ, π–X are not observed. The rapidly (n−3) narrowing structure of the nf complexes is discussed and the ionization energy accurately determined by extrapolation of selected rotational lines. Interactions between Rydberg states are numerous, s ~ d mixing produces a strong effect above n = 6 when (n + 1)s levels fuse with nl levels into 'supercomplexes'. Matrix elements are given for observed 8f ~ 9s and 6f ~ 6dδ interactions.Valence levels are not observed above the i...

The electronic spectrum of F2

Abstract: The absorption spectrum of F2 in the 780–1020 A range has been photographed at sufficient resolution to allow a rotational analysis of many bands. A large number of vibrational levels of three ionic states have been observed and their rotational constants determined. Many perturbations in the rotational structure caused by the interaction between the three states have been investigated and the interaction energies determined. The rotational and vibrational structures of a few Rydberg states have also been analyzed in detail but no Rydberg series have been identified. The difficulties in assigning the observed states are discussed. A 1Σu+ – X1Σg+ emission band system has been observed in the 1100 A region. An analysis of the bands of this system has allowed us to determine the term values and rotational constants of all the vibrational levels of the ground state with ν ≤ 22. The dissociation energy, D0(F2), is found to be greater than 12 830 and is estimated to be 12 920 ± 50 cm−1.

The absorption and emission spectra of HD in the vacuum ultraviolet

Abstract: The absorption spectrum of HD has been studied under high resolution in the vacuum ultraviolet to 840 A, the emission spectrum to 1000 A. The analysis of the latter gives accurate rotational constants and vibrational intervals of the ground state right up to the dissociation limit. Comparing these experimental data with calculations from ab initio theory, agreement to the same extent as was previously found for H2 and D2 is obtained. Extrapolation of the obs. – calc. values from H2 and D2 to infinite mass yields agreement with the recently revised theoretical values to within less than 0.1 for v < 7 and less than 0.5 cm−1 for the whole range of observed v values. The deviations for finite mass (H2 and D2) are clearly due to the non-adiabatic corrections neglected in the ab initio calculations. The results for HD are not halfway between H2 and D2 but are closer to H2. This apparent anomaly can be quantitatively accounted for, on the basis of recent calculations of Wolniewicz, by the effect of additional no...

Polymorphism in Vanadyl Phthalocyanine

Abstract: Phase transitions in vanadyl phthalocyanine have been studied using differential scanning calorimetry, x-ray scattering and optical absorption spectroscopy. Three phases, I, II and III, were prepared by nonequilibrium vapour quenching, equilibrium crystal growth and melt quenching, respectively. Phase I is metastable and transforms thermally to Phase II. Both Phase II and Phase III are stable up to the melting point. Phase II has a triclinic crystal structure isostructural with SnPc and is prone to systematic disorder in the ac plane. The disorder enhances the optical absorption at 6500 A. Attempts to account for the optical absorption spectra using simple dipole-dipole models have been unsuccessful although dimeric structures are suggested for all three phases.

The absorption spectrum of NH2 between 6250 and 9500 Å

Abstract: The earlier analysis by Dressier and Ramsay of the absorption system of NH2 has been considerably extended at the long wavelength end of the spectrum. All the low-lying vibronic levels of the excit...

Infrared observations of ices and silicates in molecular clouds

Abstract: Spectrophotometric observations from 2 to 4 microns and from 8 to 13 microns of several infrared sources associated with molecular clouds are reported. Narrow absorption features at 3.08 microns, attributed to interstellar ices, appear in all sources with a molecular cloud in the intervening line of sight. All sources showing ice absorptions also show broad absorption features, attributed to cold silicates, from 8 to 13 microns. The observed ice absorption profiles are all quite similar; however, they do not fit in detail Mie theory predictions of extinction for pure H2O or NH3 ices. The ratio of ice-to-silicate optical depths is found to vary, with most sources showing a ratio in the range 0.1-0.4. The ratio of visual extinction to ice absorption is found to increase rapidly from inside to outside the molecular cloud in NGC 2024.

NMR study of adsorbed water. I. Molecular orientation and protonic motions in the two-layer hydrate of a Na vermiculite

Abstract: The well characterized two‐layer hydrate of Na‐Llano vermiculite has been studied by continous wave (CW) wide‐line NMR and by pulse NMR of 1H nucleus in a wide temperature range. The absorption spectrum consists of a doublet and of a central line. The doublet splitting is orientation dependent between 0 and 50 °C and orientation independent below −60 °C. Below 60 °C, the symmetry of the hydration shell may be destroyed. The linewidth is compatible with rapidly rotating water molecules. An octahedral distribution of water molecules around the Na+ cations fits the experimental data, the six rotation axes around which the water molecules are spinning rapidly being tilted by about 65° with respect to the C* axis. The cation hydration shell is characterized by a rotational diffusion motion with an activation energy of 8.5 kcal, the diffusion coefficient at room temperature being about 0.5×10−8 cm2 sec−1. The diffusion coefficient of free water or protons is about 0.2×10−6 cm2 sec−1. From +50 to −100 °C, the ob...

Identification of Absorption Lines by Modulated Lower-Level Population: Spectrum of Na 2

Abstract: Molecular absorption lines from a common lower level are intensity modulated by chopped-laser saturation of another line from that level. Populations of some other levels are also modulated by subsequent fluorescence. Both types of modulated lines are free of Doppler broadening. Also, collisional depopulation modulates absorption from rotational levels near the laser-depleted level. In ${\mathrm{Na}}_{2}$, we have identified 113 lines. Analysis of the $A$ state by Kusch and Hessel is confirmed and extended.

Infrared-microwave two-photon spectroscopy: The nu 2 band of NH 3

Abstract: A spectroscopic method is developed in which the frequency of microwave radiation is added to or subtracted from that of infrared radiation by using two-photon processes in molecules. By utilizing many lines of the C${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$O lasers, this method enables us to perform systematic high-resolution spectroscopy in the 10-\ensuremath{\mu}m region. Both straightforward two-photon absorption spectroscopy and two-photon Lamb-dip spectroscopy can be used. We describe the theory of this method and its application to the observation of the ${\ensuremath{ u}}_{2}$ band of $^{14}\mathrm{N}$${\mathrm{H}}_{3}$ and $^{15}\mathrm{N}$${\mathrm{H}}_{3}$.