6533b855fe1ef96bd12b0a6f

RESEARCH PRODUCT

A Rotational Thermalization Model for the Calculation of Collisionally Narrowed Isotropic Raman-Scattering Spectra - Application to the Srs-N2 Q-Branch

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Abstract A model for the calculation of collisionally narrowed isotropic. Raman scattering spectra is proposed. In this model, the rotational transition probabilities are calculated within the strong collision approximation, allowing the rotational energy transfer rates to be expressed in terms of the sole individual Q( J ) line broadening coefficients. These transfer rates satisfy both detailed balance principle and unitarity of the scattering matrix in contrast with most of the previous approaches. Under further approximation concerning the rotational distribution of the collisional frequency, simpler expressions for transfer rates are deduced, which do not satisfy necessarily both unitarily and detailed balance. A simple analytical expression for the Q-branch profile is then obtained. An experimental study of the isotropic Q-branch for N 2 as a function of pressure has been conducted at room temperature by stimulated Raman spectroscopy (SRS). The Q-branch profiles calculated from the present model show a good agreement with SRS experiments, in particular when the lines overlap and when collisional narrowing takes place. This agreement is quite similar to that obtained by using a polynomial inverse energy gap law to describe the rotational energy transfer rates, and the results of these two models are closer for higher temperatures. The simple analytical expression mentioned above for the Q-branch profile, which is inaccurate at room temperature, becomes reliable at high temperature.