Collisional energy transfer in highly vibrationally excited H2CO(Xtilde;thinsp;1A1)

摘要

Collisional energy transfer has been investigated in highly vibrationally excited H2CO (Xtilde;thinsp;1A1) atEvibcong;11thinsp;400 cmminus;1using the method of stimulated emission pumpingndash;transient absorption spectroscopy (SEPhyphen;TAS). Total depopulation and statehyphen;tohyphen;state rate constants were measured for several rotational levels of the 2444vibrational state. For H2CO selfhyphen;relaxation the depopulation rate constant of the 61,5level was measured to bek0=(3.12plusmn;0.13)times;10minus;9cm3/moleculethinsp;s. An analysis of the statehyphen;tohyphen;state data with a simplified master equation approach yielded rate constantsk1=(7.7plusmn;1.2)times;10minus;10,k2=(1.2plusmn;0.3)times;10minus;10, andk3=(0.6plusmn;0.3)times;10minus;10cm3/moleculethinsp;s for collisions with Dgr;J=1, 2, and 3, respectively, and Dgr;Ka=0, Dgr;Kc=Dgr;J, the reverse rate constants being given by microscopic reversibility. Thus, the Dgr;J=plusmn;1 steps account for sim;50percnt; of all inelastic collisions, which can be rationalized in terms of a simple dipolendash;dipole interaction. AtEvibcong;11 400 cmminus;1, where rgr;vibcong;0.42/cmminus;1, collisions seem to conserve the vibrational character in spite of the fact that the energy gap between adjacent vibrational states is a fraction of the transferred rotational energy.