Michael H. Proffitt

Absolute cross sections for collision-induced scattering of light by binary pairs of argon atoms

Absolute intensities of the collision-induced Raman spectrum of argon are measured relative to certain rotational Raman lines of known intensity in hydrogen and nitrogen. Using the 4880 A laser line for excitation and a detector sensitive to both polarizations, at a frequency shift of -12 wavenumbers, the cross section times unit volume and per unit wavenumber band, for scattering of light at right angles by binary pairs of argon atoms, is found to be 2·89 × 10-53 cm6±7 per cent. Rigorous wave-mechanical computations on the basis of Placzeks polarizability theory predict a value of 2·83 × 10-53 cm6±2 per cent and reproduce the experimental spectrum from about 6 to 60 wavenumbers, if the empirical MSV III potential is used together with the point-dipole model of the anisotropy of the polarizability tensor of two interacting atoms. For comparison, computations based on the rigorous classical trajectories of the collisions are presented. If the same potential function and model of the anisotropy are employe...

About the anisotropy of the polarizability of a pair of argon atoms

Available models of the anisotropy of the polarizability of a pair of argon atoms are used to compute the collision-induced Raman spectrum. It is seen that the point-dipole model allows the best fit of the experimental frequency distribution and absolute intensity, which have been measured previously. Other models of the anisotropy appear by these criteria to be overcorrected or, if successful, not significantly different from the point-dipole expression.

Absolute cross sections for collision-induced depolarized scattering of light in krypton and xenon

Depolarized Raman spectra of binary collisional pairs of atoms in krypton and xenon are obtained at gas densities of 1–10 amagat. Absolute intensities relative to a known rotational transition of nitrogen are determined. For light of 4880 A wavelength incident in the x-direction, polarized in the z-direction and scattered in the y-direction of a cartesian frame x, y, z, at a frequency shift of -12 cm-1, the differential scattering cross section per unit wavenumber band times volume, is found to be 1·10 × 10-52 cm6 ± 10 per cent for krypton, and 4·76 × 10-52 cm6 ± 10 per cent for xenon, if the sum of both polarizations is considered. Wave-mechanical and classical computations reproduce both the shape and the intensity of the experimental spectra if the so-called point-dipole model of the anisotropy of the polarizability of collisional pairs of atoms is used. Other models of the anisotropy are seen to be overcorrected by these criteria.

The collision‐induced polarized and depolarized Raman spectra of helium and the diatom polarizability

The spectral distributions and absolute intensities of collision‐induced Raman spectra of helium are obtained at 30 amagat, with incident beam polarizations parallel and perpendicular to the observation. These spectra can readily be separated into the polarized and the depolarized Raman continuum of the helium diatom. For comparison, spectra are also computed from wave mechanics, on the basis of Placzeck’s polarizability theory. Accurate, semiempirical interaction potentials are used as input, together with ab initio computations of the helium diatom polarizability tensor components. The computed spectra of selected trace and anisotropy functions agree with the observed polarized and depolarized continua. Anisotropy functions consistent with the depolarized spectrum differ by less than 5% from the classical dipole‐induced dipole (DID) values at 2.685 A separation.

Cross sections for reorientation and rotational relaxation of oxygen

Experimental measurements of the collisional EPR linewidths of molecular oxygen are reported for 17 X‐band transitions at resonance magnetic fields up to 0.7 T. In addition to the expected gradual decrease of linewidth with rotational quantum number, a dependence upon orientation quantum number is also observed. The EPR linewidths are comparable to the higher values among the microwave results previously reported for the 60 GHz transitions and substantially larger than the corresponding Raman data.

Concerning the anisotropy of the helium diatom polarizability

The spectral distribution and absolute intensity of the collision‐induced Raman spectrum of He is measured and compared to wave mechanical calculations. (AIP)

The polarized Raman spectrum of the argon diatom

The first measurement of the polarized Raman spectrum of the argon diatom are reported. The existing theoretical models of the diatom are discussed. (AIP).

Collision-induced raman scattering by anisotropic molecules (H2, D2)☆

Abstract The collision-induced translational Raman spectra of hydrogen and deuterium are measured on an absolute intensity scale and compared with theoretical profiles based on the dipole-induced-dipole (DID) model of the pair polarizability. The DID model reproduces fairly closely the measured spectra, which are nearly fully depolarized.

Collisional linewidths of the EPR spectrum of molecular oxygen

Pressure broadening of the X‐band EPR spectrum of molecular oxygen was studied in an apparatus designed to minimize systemtic and random errors in the collisional linewidth. Results are reported for 16 lines with rotational quantum number N ranging from 1 to 11. No explicit M dependence of linewidth at the 1% accuracy level was found except that the N = 1, J = 1 line with initial M value of 0, which is at a substantially higher field than the other N = 1 lines, was found to be significantly broader than the other N = 1 lines. Otherwise, a slight but definite decrease of width with increasing field was found, presumably due to magnetic alignment of O2. Over the 0.5 to 2.3 Torr pressure range studied there was a remarkable variation of width with pressure, implying a small negative linewidth at zero pressure, for which we were unable to find a satisfactory explanation in theory or systematic measurement errors.

Concerning the anisotropy of the polarizability tensor of pairs of methane molecules

Abstract The depolarized Raman spectrum of collisional pairs of methane molecules is obtained over a range of intensities exceeding two orders of magnitude, and at densities low enough (1.8 amagat) to suppress all three-body contributions. Absolute intensities are determined relative to a nitrogen rotational Raman line of known intensity. The experimental spectrum is reproduced from theory in all detail if the dipole-induced dipole (DID) approximation of the anisotropy of the pair polarizability tensor is used. Other models of the anisotropy are inconsistent with experiment unless they differ by less than about 5% near 3.82Ainternuclear separation.