H. J. Bernstein

Resonance Raman Effect and Resonance Fluorescence in Halogen Gases

The various output frequencies of the argon ion laser at 5145, 5017, 4965, 4880, and 4765 A lie in the absorption bands of the heavier halogen gases. With the appropriate choice of exciting line, either resonance Raman effect or resonance fluorescence can be observed. The difference between the two types of spectra are discussed in some detail. In the case of a strong resonance Raman effect, overtone sequences up to the 14th harmonic could be observed. Raman frequencies, depolarization ratios, and relative scattering cross sections are given for the fundamentals and overtones of Cl2, Br2, I2, BrCl, ICI, and IBr at 4880 A excitation.

Gas Phase Raman Intensities: A Review of “Pre-Laser” Data

Raman radiant intensities and depolarization ratios measured for gases with mercury arc irradiation and photoelectric detection have been collected. The observed intensities have been reduced to values of the scattering activity, gj(45α j ′2+7γ j ′2). The scattering activity and Raman scattering cross sections are explicitly related. Data for strong sharp bands are accurate to about ± 5% – 10%, while data for weak and broad bands are less accurate.

A Cell for Resonance Raman Excitation with Lasers in Liquids

The experimental observation of the resonance Raman effect in solutions with laser excitation is restricted by the absorption of the sample. Due to the thermal lens effect it is not possible to get a sharp laser focus in highly absorbing media. Under ordinary circumstances one is required to compromise between absorption and emission of the scattered light—that means discovering optimal solution concentrations and suitable laser power or focusing conditions to get the smallest degradation of the laser beam.

The UV-laser excited resonance raman spectrum of the I−3 ion☆

Abstract Solutions of cesium tri-iodide and potassium iodide and iodine in water show 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. This progression allows the confirmation of the presence of the I−3 ion in iodine-methanol solutions.

INTENSITY IN THE RAMAN EFFECT

Abstract A method is described for obtaining high quality photoelectrically recorded Raman spectra of gases at pressures of 1 to 2 atmospheres. Sufficient intensity was obtained by the use of a multiple reflection cell and six watercooled mercury arcs, each carrying 20 amp. All the corrections required for obtaining true intensities and depolarization ratios from those observed were evaluated experimentally. Comparison of the theoretical values of intensity ratios of hydrogen rotational lines, the H 2 and D 2 vibrational lines, and the depolarization ratio of the symmetrical CC stretching band of neopentane with those observed in the present setup (after being corrected) show that the method presented for obtaining the true intensity is not in error by more than a few percent. The intensitites and depolarization ratios of the Raman bands for some simple molecules were measured. It was possible to assign the Raman spectrum of the bands in the 1950-cm −1 region in acetylene from intensity considerations, and a definitive value for the anharmonicity constant X 24 is obtained and an upper limit given for X 25 . A simple model is discussed by which the Raman intensity of the totally symmetrical stretching band in the hydrides H n Y , and the polarizabilities of these molecules, may be estimated. The present theory of the Raman effect is applicable only to molecules in the gas phase at relatively low pressure. Gas spectra have been obtained photographically where long exposure can compensate for the weak intensity of the Raman scattering, however, such spectra yield, in general, poor Raman intensity data. The photoelectric method of recording Raman spectra of gases is a more accurate means of obtaining the intensities of the Raman bands, but it has been difficult to put into practice because of the low intensity of the Raman scattering. In the first part of this work a method is described for obtaining photoelectrically recorded Raman spectra of gases of sufficiently high quality to make possible good intensity and depolarization measurements. In the second part, the results for some simple molecules are presented and discussed.

Rotational isomerism. XI. Raman spectra of n‐butane, 2‐methylbutane, and 2, 3‐dimethylbutane

Raman spectra have been obtained for n‐butane, 2‐methylbutane, and 2, 3‐dimethylbutane in the vapor and solid (−196°C) phases. The low temperature spectra of the solids undergo a marked simplification due to the disappearance of all but one of the rotational isomers. This enabled band pairs in the vapor spectrum to be identified with the appropriate rotational isomers. From the temperature dependence of selected band pairs the enthalpy difference between the rotational isomers was obtained for each compound in the vapor phase.

Rotating Raman Sample Technique for Colored Crystal Powders; Resonance Raman Effect in Solid KMnO4

A simple sample technique which makes it possible to record Raman spectra of highly absorbing solids is described. The main feature is a rotating sample system containing pressed crystal powders, on which the laser beam is focused. The relative motion between laser focus and sample surface avoids heating and decomposition of the crystal powder. With this technique it is, for instance, possible to obtain a Raman spectrum of solid potassium permanganate, displaying a progression of strongly resonance enhanced overtones of the totally symmetric permanganate mode as well as a well-defined weakly enhanced spectrum for the other internal modes.

The resonance Raman effect of the permanganate and chromate ions

Resonance Raman spectra have been obtained from the MnO4 - and CrO4 2- ions in aqueous solutions and as solid. High intensity overtone progressions of the totally symmetric vibration v 1 were observed, allowing estimates of the anharmonicity constants and harmonic frequencies to be made for the v 1 breathing mode. Relative intensities have been measured in the resonance case and correlated with the absorption spectra. Also preresonance intensity data for CrO4 2- have been determined and discussed in terms of an existing theory. The overtone progression of v 1 shows a large increase in half-bandwidth with increasing vibrational quantum number.

Intensity in the Raman effect. IX. Absolute intensities for some gases and vapors

The experimental procedure of Yoshino and Bernstein for the measurement of Raman intensities of gases has been simplified and the apparatus adapted to the investigation of the spectra of vapors. For absolute intensities the pure rotation line J = 1 → 3 of hydrogen was used as an internal standard as suggested by Golden and Crawford. A method for the determination of depolarization ratios is described. The value obtained for the polarizability derivative of methane agrees with previous measurements. Absolute Raman intensities are given for the strong bands of ethane, propane, n-butane, n-pentane, n-hexane, cyclohexane, benzene, carbon tetrachloride, carbon disulfide, chloroform, acetonitrile, methanol, methyl bromide, methyl chloride, acetylene, and vinyl acetylene, and depolarization ratios for benzene, carbon disulfide, acetylene, and vinyl acetylene. The intensities of the CH stretching vibrations of the n-alkanes from propane to n-hexane increase linearly within ±5%. A comparison of the intensity of the ν1 band of carbon tetrachloride in the vapor and in the liquid shows, that the intensity is enhanced in the liquid by a factor of at least 1.7, due to intermolecular interactions. A comparison is made of the standard intensities and depolarization ratios in the gaseous and in the liquid phase.

Raman spectra of negative molecular ions doped in alkali halide crystals

Abstract Raman bands arising from S 2 − and S 3 − have been observed in alkali halide single crystals which had been heated in the presence of sulphur vapor. The S 3 − ion could also be detected in the mineral ultramarine. Since the excitation frequency was sometimes close to the absorption band of these species, a resonance Raman effect was observed. This was strongest for the S 3 − species in KCl where the fifth overtone of the symmetrical stretching mode vibrational could be seen. In similarly treated crystals, the vibrational Raman bands of Se 2 − and SeS − were observed. Raman data for N 2 − in potassium halide single crystals are also reported.