Relaxation of H_2O from its |04 ~- vibrational state in collisions with H_2O,Ar,H_2,N_2,and O_2

摘要

We report rate coefficients at 293 K for the collisional relaxation of H_2O molecules from the highly excited |04>~(+-) vibrational states in collisions with H_2O,Ar,H_2,N_2,and O_2.In our experiments,the |04>~- state is populated by direct absorption of radiation from a pulsed dye laser tuned to approx 719 nm.Evolution of the population in the (04>~(+-)) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser,which selectively photolyses H_2O(|04>~(+-)),and a frequency-doubled dye laser,which observes the OH(upsilon=0) produced by photodissociation via laser-induced fluorescence.The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays.The rate coefficients for relaxation of H_2O(|04>~(+-)) obtained from these experiments,in units of cm~3 molecule~(-1) s~(-1),are: k(H_2O)=(4.1+-1.2)X10~(-10),k(Ar)=(4.9+-1.1)X10~(-12),k(H_2)=(6.8 +-1.1)X10~(-12),k(N_2)=(7.7+-1.5)X10~(-12),k(O_2)=(6.7+-1.4)X10~(-12).The implications of these results for our previous reports of rate constants for the removal of H_2O molecules in selected vibrational states by collisions with H atoms (P.W.Barnes et al,Faraday Discuss.Chem.Soc.113,167 (1999) and P.W.Barnes et ai,J.Chem.Phys.115,4586 (2001).) are fully discussed.