The method of laserhyphen;excited vibrational fluorescence is used to measure the vibrational relaxation rates of H2thinsp;18O in collisions with H2thinsp;18O, Ar, N2, and O2. Pumping of various vibrationndash;rotation lines of the ngr;1and ngr;3stretching levels with a tunable infrared laser leads to the same measured rate constants. In pure H2thinsp;18O the stretching levels are found to relax together with a rate constant of 2.2times;10minus;11cm3moleculeminus;1secminus;1, the bend overtone relaxes with a rate constant of 9.1times;10minus;11cm3moleculeminus;1secminus;1, and the bend fundamental relaxes with a rate constant between 5times;10minus;11and 9times;10minus;11cm3moleculeminus;1secminus;1. Relative intensity measurements show that the dominant relaxation pathway isVrarr;Vtransfer from the stretching vibrations to thev2=2 bending level followed by stepwiseVrarr;T,Rrelaxation tov2=1 and thenv2=0.
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