An experimental and numerical study of high-frequency Raman scattering in argon gas

Accurate pair‐anisotropy models out of a set of input experimental moments via a novel non‐linear inversion method

“…Careful measurements of its Stokes spectrum in the broad interval 2-400 cm 1 have been reported in the past by our group. 12 From subsequent theoretical studies by the group, the long-ago reported Dacre's ab initio anisotropy 13 has been found 14,15 to reproduce the experimental bandshape well, but is inconsistent with measurements in the interval 150-350 cm 1 (outside error bars). Given this inadequacy, the question is now raised of whether our inversion method is capable of providing a semiempirical model that improves that of Dacre, yielding spectra that fit experimental data with maximum accuracy.…”

“…The method was applied to the Ar 2 depolarized spectrum, recorded previously by our group over a broad spectral domain. 12 A semiempirical anisotropy model for the atomic pair was determined, accounting effectively for short-range effects that were missing in the previously computed ab initio models. 13,17 As the main advantages, our method is distinguished for its adaptability to any given functional form ofˇ(or of any other polarizability invariant), its easy numerical implementation, its rapid convergence (with nearly infinite accuracy) to the input moments, its simultaneous convergence to all unknown parameters and its extensibility to an arbitrary number of unknowns.…”

High-frequency interaction-induced rototranslational wings of isotropic nitrogen spectra

“…For Oc -0, we have a = 0, b = 7/6, c = d = 1. From equations (58) and (59) rotational lines of nitrogen gas at low densities [54] and the binary interactioninduced scattering of argon gas [49] for a frequency shift v = 20 cm-1. Then, for each frequency shift considered, from the measurement of the depolarization factor q,(v) and from equation (61), the isotropic intensities I~so(V) were obtained in absolute units.…”

“…We used a scattering experimental set-up which has been described elsewhere [13,49]. The intensities scattered by the nitrogen gas were measured using an argon laser beam (541-5 nm, 2 W) to illuminate the gas contained in a four-window high pressure cell.…”

“…In order to obtain the intensities in absolute units we preliminarily calculated the depolarized intensities D(v) induced by collisional pairs of nitrogen molecules in absolute units by comparison with the depolarized scattering intensities of reference lines[49, 53]. We used two types of reference intensities: the intensities of scattering Downloaded by [UQ Library] at 17:The rototranslational experimental isotropic double differential cross-section (dzcr/ ~-Q ~c0)iso of N 2 at 295 K in the frequency range 300-600 cm -1.…”