CARS Measurement on Excited States of Gas Molecules

Abstract

The CARS intensity and spectral width were measured for light simple and heavy polyatomic molecules at the under-atmospheric gas pressure (50-760 Torr). The observed ratios of Raman cross section were 1: 1.3: 0.53 for N₂: CO₂: SF₆, in agreement with the previous data. The collisional narrowing effect was found even at low gas pressure of CO₂ 400 Torr and of SF₆ 50 Torr while only the pressure broadening was observed in N₂ CARS of this pressure range. The N₂ gas additive enhanced much the CARS intensity rather than the He .The SF₆ infrared active (ν3) mode excitation by a CO₂ 10.6μm laser irradiation reduced the CARS intensity of the ν1 mode but enhanced its hot bands. It was deduced from the different reduction effect of the CARS intensity between its P (20) and P (28) line irradiation that the N₂ gas plays an important role as vibrational-rotational energy reservoir for the SF₆ gas molecules excited in the quasi-continuum.