The study of the D′ 1Πu state of H2:: Transition probabilities from the ground state, predissociation yields, and natural linewidths

The absorption spectrum of the H-2 molecule was studied at high resolution in the 81-72 nm spectral range. A detailed analysis of the D' (1)Pi(u)-> X (1)Sigma(+)(g) electronic band system is reported. In the spectrum, more than 70 new lines were assigned. For wavelengths longer than 75 nm, the D' (1)Pi(+)(u) and (1)Pi(-)(u) components show a clearly different behavior: Tau he (1)Pi(+)(u) one dissociates into H(1s)+H(n=2) whereas the (1)Pi(-)(u) one leads to molecular fluorescence. For shorter wavelengths, both components are predissociated into H(1s)+H(n=3). The predissociation yields, the dissociation widths, and the absolute values of the transition probabilities were measured over the vibrational progression from v'=3 to 17, i.e., up to the dissociation limit. The comparison between these absolute transition probabilities and the values calculated in the adiabatic and nonadiabatic approximations demonstrates clearly the importance of nonadiabatic couplings.