Quantitative estimation of collisional dephasing rate in the X1A1–A1A2 (410) band of formaldehyde with degenerate four wave mixing spectroscopy

Abstract

AbstractThe application of degenerate four wave mixing (DFWM) spectroscopy to the study of collisional dephasing in the 1A2(410) excited band of formaldehyde has been carried out. The method relies on the measurement of DFWM signal dependence on the partial pressures of different buffer gases and in the saturated regime. Experiments were conducted with CO2, N2 and He as colliding partners to H2CO, and collisional dephasing rates γpd of the order of 1010 s−1 atm−1 were estimated. The experimental findings clearly indicate that coherence decay is the dominant mechanism, with respect to rotational energy transfer (RET), in determining the DFWM signal decreasing with pressure. The comparison between the different values of γpd measured and the literature data for γRET has been used to shed light on key factors mostly ruling the competition between decoherence and population relaxation effects. Copyright © 2007 John Wiley & Sons, Ltd.