Retrieval of Total Scattering Cross Sections of Molecules from Inhomogeneously Broadened Absorption Lines

V P Kochanov,L N Sinitsa

doi:10.1155/2018/2098625

Abstract

A new method of retrieving quantitative information on the hard, soft, and diffraction collision’s frequencies from inhomogeneously pressure-broadened line profiles was proposed and tested. The essence of the method lies in the processing of recorded profiles using various profiles’ models containing these frequencies treated as adjustable parameters in different manners. Three self-broadened H2O absorption lines free of an instrumental function were processed with the use of four model line profiles. Retrieved set of pressure line broadening and narrowing constants allows finding out the sought frequencies. The estimation of the total scattering cross section, ∼630 Å2, in pure water vapor was made.

Highlights

Various models for spectral line profiles allow retrieving information on collision processes that affect the line shape.e simplest Lorentzian and Voigt profiles provide retrieving only the homogeneous collision line half-width c and the line shift Δ
With the aid of more complicated profiles [1,2,3,4], where the Dicke line narrowing [5, 6] is taken into account, it is possible to find out an additional parameter—the frequency of elastic velocity-changing collisions
Where v is the most probable thermal speed of absorbing molecules. us, exploitation of the collision line narrowing makes it possible to obtain the data on D from processing recorded line profiles, which is still nonconventional information for spectroscopy

Summary

Introduction

Various models for spectral line profiles allow retrieving information on collision processes that affect the line shape. Certain parameters may have a direct physical meaning, and they can serve as a source of valuable additional information extracted from a line shape Such are the frequencies of soft and hard velocity-changing collisions. Is opens a possibility to retrieve the newly introduced parameters from processing experimental line profiles It was shown earlier [12,13,14] that the output frequency ]t can be measured directly as a collision-broadening constant of nonlinear resonances at sufficiently low gas pressures. Correct account of the combined effect of hard and soft collisions [8,9,10,11] performed on the basis of the quantum-mechanical collision integral kernel [7] and the inverse-power intermolecular interaction potentials provides the presence of all the frequencies specified in (2) in the model line profiles [8,9,10,11]. Parameters of these lines taken from [18] are presented in Table 1. e self-broadening of these lines was registered within the pressure range 1 Torr ≤ p ≤ 20 Torr

Data Processing e following line profiles have been used in data processing:

Findings

Discussion and Conclusions