Non-adiabatic transitions from I2(E0g+ and D0u+) states induced by collisions with M = I2(X0g+) and H2O

The stepwise two-step two-color and three-step three-color laser excitation schemes are used for selective population of rovibronic levels of the first-tier ion-pair E0(g)(+) and D0(u)(+) states of molecular iodine and studies of non-adiabatic transitions to the D and E states induced by collisions with M = I-2(X) and H2O. Collection and analysis of the luminescence after excitation of the upsilon(E) = 8, 13 and upsilon(D) = 13, 18 vibronic levels of the E and D states in the pure iodine vapor and the gas-phase mixtures with H2O provide rate constants for the non-adiabatic transitions to the D and E state induced by collisions with these molecules. Vibrational distributions for the I-2(E, upsilon(E) (M)<-> D, upsilon(D)) collision-induced non-adiabatic transitions (CINATs) are obtained. Rather strong lambda(max)(lum) approximate to 3400 angstrom luminescence band is observed in the I-2 + H2O mixtures, whereas its intensity is similar to 100 times less in pure iodine vapor. Radiative lifetimes and quenching rate constants of the I-2(E,nu(E) = 8, 13 and D,nu(D) = 13, 18) vibronic state are also determined. Rate constants of the I-2(E, upsilon(E) (I2(X))-> D, upsilon(D)), upsilon(E) = 8-54, CINATs are measured again and compared with those obtained earlier. New data confirm resonance characters of the CINATs found in our laboratory about 10 years ago. Possible reasons of differences between rate constant values obtained in this and earlier works are discussed. It is shown, in particular, that differences in rate constants of non-resonant CINATs are due to admixture of water vapor in iodine. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725541]