Transient population distribution of SF6 gas excited by a CO2 laser

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Abstract
A method is developed for the calculation of the transient molecular population distribution of a gas excited by a laser pulse or any other means. This method allows the calculation of the vibrational energy distribution from the observed infrared fluorescence or absorption spectrum, and vice versa. First, two sample calculations for SF6 were performed: one in which the weak intensity absorption spectrum at 300 K was calculated using a thermal population distribution function (PDF), and the results were compared to the measured data, and the other in which the measured spectrum was used to calculate the PDF and the results were compared to the thermal PDF. Satisfactory agreement was obtained in both cases. Then we calculated the PDF of SF6 from its infrared fluorescence spectrum which was measured immediately after a CO2 laser excitation. The results show that at fairly low excitation levels (〈n〉≊1.5) there is a nonthermal PDF in the gas, which has a prominent maximum at high vibrational energies in addition to the maximum at low energies.