Energies, transition probabilities, predissociation rates, and lifetimes of the H2, HD, and D2 c 3Πu- state

Transition probabilities of H-2, HD, and D-2 c (3)Pi(-)(u) -a (3)Sigma(+)(g) electric dipole, c (3)Pi(-)(u) -b (3)Sigma(+)(u) discrete-continuum magnetic dipole, and electric quadrupole transitions have been calculated using accurate energies and ro-vibrational wave functions obtained from precise ab initio potential energy curves. The predissociation rates of the c (3)Pi(-)(u) (v, N) levels by direct and indirect spin-spin and spin-orbit coupling between c (3)Pi(u) -b (3)Sigma(+)(u) fine structure levels, have been also determined. The present investigation achieved good agreement with measured lifetimes of the c (3)Pi(-)(u) fine structure levels without adjustment. A comparison of the calculated and observed lifetimes of metastable H-2, HD, and D-2 suggests that the c (3)Pi(-)(u) -b (3)Sigma(+)(u) magnetic dipole and electric quadrupole transition moments underestimate the spontaneous emission rate of the metastable levels by similar to 370 s(-1). The measured and calculated lifetimes of H-2, HD, and D-2 fine structure levels are in very good agreement after the adjustment of 370 s(-1) to the spontaneous decay rate of the c (3)Pi(-)(u) -b (3)Sigma(+)(u) transition. The calculated energies, transition probabilities, and predissociation rates obtained in the present work, along with the c (3)Pi(u) state excitation function, are sufficient to determine the c (3)Pi(u) state emission cross section, the kinetic energy distribution of H(1s) atoms, and the energy deposition rate of the (1)Sigma(+)(g) -c (3)Pi(u) excitation. In a previous investigation by Berg and Ottinger (1994 J. Chem. Phys. 100 8746), the authors were forced to insert a large scale factor into the predissociation rate in order to reconcile with measured lifetimes. Errors introduced in the approximations made in the previous investigations are discussed in the text. The H-2 c (3)Pi(u) state has the second largest triplet state excitation cross section. Predissociation and spontaneous emission of the c (3)Pi(u) state plays an important role in the energy deposition of H-2-dominated atmospheres.