Radiative association of He{sup +} with H{sub 2} at temperatures below 100 K
- Institute of Physics, Nicolaus Copernicus University, Grudziadzka 5, PL 87-100 Torun (Poland)
The paper presents a theoretical study of the low-energy dynamics of radiative association processes in the He{sup +}+H{sub 2} collision system. Formation of the triatomic HeH{sub 2}{sup +} ion in its bound rotation-vibration states on the potential-energy surfaces of the ground and of the first excited electronic states is investigated. Close-coupling calculations are performed to determine detailed state-to-state characteristics (bound<-free transition rates, radiative and dissociative widths of resonances) as well as temperature-average characteristics (rate constants, photon emission spectra) of the two-state (X<-A) reaction He{sup +}({sup 2}S)+H{sub 2}(X{sup 1}{sigma}{sub g}{sup +}){yields}HeH{sub 2}{sup +}(X{sup 2}A{sup '})+h{nu} and of the single-state (A<-A) reaction He{sup +}({sup 2}S)+H{sub 2}(X{sup 1}{sigma}{sub g}{sup +}){yields}HeH{sub 2}{sup +}(A{sup 2}A{sup '})+h{nu}. The potential-energy surfaces of the X- and A-electronic states of HeH{sub 2}{sup +} and the dipole moment surfaces determined ab initio in an earlier work [Kraemer, Spirko, and Bludsky, Chem. Phys. 276, 225 (2002)] are used in the calculations. The rate constants k(T) as functions of temperature are calculated for the temperature interval 1{<=}T{<=}100 K. The maximum k(T) values are predicted as 3.3x10{sup -15} s{sup -1} cm{sup 3} for the X<-A reaction and 2.3x10{sup -20} s{sup -1} cm{sup 3} for the A<-A reaction at temperatures around 2 K. Rotationally predissociating states of the He{sup +}-H{sub 2} complex, correlating with the {upsilon}=0, j=2 state of free H{sub 2}, are found to play a crucial role in the dynamics of the association reactions at low temperatures; their contribution to the k(T) function of the X<-A reaction at T<30 K is estimated as larger than 80%. The calculated partial rate constants and emission spectra show that in the X<-A reaction the HeH{sub 2}{sup +}(X) ion is formed in its highly excited vibrational states. This is in contrast with the vibrational state population of the ion when formed via the (X<-X) reaction He({sup 1}S)+H{sub 2}{sup +}(X{sup 2}{sigma}{sub g}{sup +}){yields}HeH{sub 2}{sup +}(X{sup 2}A{sup '})+h{nu}.
- OSTI ID:
- 20722876
- Journal Information:
- Journal of Chemical Physics, Vol. 122, Issue 22; Other Information: DOI: 10.1063/1.1924453; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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