Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)

TL;DR

This technical report recommends the Hartmann--Tran profile as a superior, physically accurate line shape model for high-resolution spectroscopic data, replacing the traditional Voigt profile.

Contribution

It introduces the Hartmann--Tran profile as a new, comprehensive line shape model for high-resolution spectroscopy, improving accuracy over the Voigt profile.

Findings

Hartmann--Tran profile captures pressure effects more accurately.

The profile can be computed efficiently and reduces to simpler models.

It addresses inadequacies of the Voigt profile in high-resolution spectra.

Abstract

The report of an IUPAC Task Group, formed in 2011 on "Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory" (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule have resulted in the development of a variety of alternative line-profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially Correlated quadratic-Speed-Dependent Hard-Collision profile should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann--Tran profile (HTP). The HTP is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions.