Deactivation of Iast; (ast;=2P1/2) by three isotropic forms of hydrogen has been monitored both by observing the decay of Iast; emission at 1.315 mgr;m and by probing theErarr;Vtransfer from Iast; to hydrogen indirectly through observation of subsequentVrarr;Vtransfer from hydrogen to CO2. Iast; is relaxed by H2, HD, and D2at rates of (3.69plusmn;0.22) times;103secminus;1thinsp;Torrminus;1, (9.5plusmn;1.3) times;103secminus;1thinsp;Torrminus;1, and 45plusmn;14 secminus;1thinsp;Torrminus;1, respectively. The minimum number of hydrogen vibrational quanta excited per deactivation of Iast; has been calculated from the amplitude ratio of CO2(mn1)/Iast; fluorescence. These minima are 0.61plusmn;0.12 for HD, 0.51plusmn;0.10 for H2, and 0.10plusmn;0.03 for D2. The actual values may be higher due to uncertainties in corrections for radiative trapping and in the analysis of the kinetic scheme. The current results are compared to the predictions of recent quantum mechanical calculations.
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