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An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, and transport phenomena in dilute gases. The computation of spectral line profiles corresponding to those obtained from ultra-high-resolution spectral line-shape measurements requires numerical ab initio calculation of scattering amplitudes directly from the underlying dynamics of collisions between radiatively active molecules and their perturbers. The Wigner distribution function-density matrix is utilized to describe the kinetic theory of spectral line shapes and to discuss the various collisional processes that contribute to the kernel of kinetic equations. The influence of features of the potential energy surface on spectral parameters is also discussed, and the importance of comparing experimental line profiles directly with numerically computed line shapes obtained from reliable interaction potentials is emphasized. This contrasts sharply with the universal practice of comparing experimental line widths and shifts using some average or approximate theoretical scattering cross- sections and it contrasts sharply with fitting experimental profiles to some convenient analytical line-shape model; hence the phrase 'a paradigm shift' in the title of this work. PACS Nos.: 32.70.Jz, 33.20.-t, 33.70.Gj, 34.50.-s. Nous avons presente une revue de la theorie du profile de raies spectrales suite a des collisions binaires, de facon a developper une approche unifiee de mecanique statistique pour la theorie du profile de raie, l'optique non lineaire, la theorie des lasers et les phenomenes de transport dans les gaz dilues. Le calcul du profil des raies spectrales qui correspondent a ces mecanismes exige un calcul ab initio des amplitudes de diffusion directement a partir de la dynamique des collisions entre des molecules a impact radiatif et les mecanismes perturbateurs. Nous couplons la fonction de distribution de Wigner et la matrice de densite pour decrire la theorie cinetique du profile de raie spectrale et discuter les differents mecanismes de collision qui contribuent au noyau des equations cinetiques. Nous analysons egalement l'influence des particularites de la surface d'energie sur les parametres spectraux et nous insistons sur l'importance de comparer les profiles experimentaux de raie directement avec les profiles de raie calcules a partir de potentiels fiables. Ceci contraste nettement avec la pratique universelle ou on compare les valeurs experimentales des largeurs et deplacements de raie en utilisant des sections efficaces approximatives quelconques, theoriques ou moyennes et contraste nettement avec l'ajustement des profiles de raie experimentaux a une forme analytique commode; d'ou l'expression << un changement de paradigm >> dans le titre. [Traduit par la Redaction], 1. Introduction The impact theory of spectral line shapes has been around for about a century, beginning with the classical theory of Lorentz [1], and was essentially completed with the [...]

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An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, and transport phenomena in dilute gases. The computation of spectral line profiles corresponding to those obtained from ultra-high-resolution spectral line-shape measurements requires numerical ab initio calculation of scattering amplitudes directly from the underlying dynamics of collisions between radiatively active molecules and their perturbers. The Wigner distribution function-density matrix is utilized to describe the kinetic theory of spectral line shapes and to discuss the various collisional processes that contribute to the kernel of kinetic equations. The influence of features of the potential energy surface on spectral parameters is also discussed, and the importance of comparing experimental line profiles directly with numerically computed line shapes obtained from reliable interaction potentials is emphasized. This contrasts sharply with the universal practice of comparing experimental line widths and shifts using some average or approximate theoretical scattering cross-sections and it contrasts sharply with fitting experimental profiles to some convenient analytical line-shape model; hence the phrase 'a paradigm shift' in the title of this work. [ABSTRACT FROM AUTHOR]