Abinitiostudy of electronic energy transfer in the quenching of N2(Athinsp;3Sgr;+u) and N2(Bthinsp;3Pgr;g) by H2

摘要

The interactions of N2(Athinsp;3Sgr;+u) and N2(Bthinsp;3Pgr;g) with H2(Xthinsp;1Sgr;+g) have been characterized through potential energy calculations, which were performed using a combination of MCSCF and multiplehyphen;reference SDCI methods. InC2vgeometry with the N2and H2bond axes parallel, at the highest level of theory used, energy transfer from N2(Athinsp;3Sgr;+u) to H2(bthinsp;3Sgr;+u) and dissociation of the latter into H atoms is found to proceed through an adiabatic reaction path with a barrier of 0.513 eV. InC2vgeometry with perpendicular orientation of N2and H2, the two lowest3B2surfaces are shown to exhibit a strongly avoided crossing; the lower surface shows a favorable pathway for energy transfer from N2(Bthinsp;3Pgr;g) to H2(bthinsp;3Sgr;+u). In each case, energy transfer occurs via a twohyphen;electron exchange mechanism as a result of mixing between orbitals with the proper energy and symmetry. Consistent with the isoconfigurational electronic structure of N2(B) and CO(athinsp;3Pgr;), the results for N2(B) are similar to those which we found previously for quenching of CO(a) by H2. The overall results are shown to be consistent with available experimental kinetics data, which show quenching of N2(A) by H2to be inefficient. Application of these results to electronic quenching and vibrational relaxation of N2(A) by other small molecules is discussed.