Resonance-enhanced two-photon dissociation of H-2 through nonadiabaticallycoupled intermediate and final states

Nonperturbative time-dependent calculations of the resonance-enhanced two-p hoton dissociation probability of H-2 in two frequency laser fields from th e ground X (1)Sigma(g)(+) (upsilon = 0, j = 0) level to the final continua of GK (1)Sigma(g)(+) and I (1)Pi(g) states have been made as functions of t he laser frequencies. The two fields are taken to have linear parallel pola rizations with identical sine-squared time dependences of the amplitudes. T he first held of frequency omega(1) is near resonant with the two closely s paced excited intermediate levels B (1)Sigma(u)(+) (u = 14, j = 1) and C (1 )Pi(u)(+) (upsilon = 3, j = 1), which are strongly coupled to each other th rough nonadiabatic interaction as well as by radiative Raman coupling. Thus two intermediate levels with mixed Sigma(+)-Pi(+) character are created. T he molecule finally dissociates through coherent excitation to a number of near-resonant discrete rovibrational bound levels of H (H) over bar (1)Sigm a(g)(+) and J (1)Delta(g)(+) embedded into the continua of GK and I states as well as by direct transition to these continua, by absorption of a secon d photon of frequency oz. The nonadiabatic interactions of the bound levels of H (H) over bar and J states, with the respective continuum of GK and I states, give these levels a predissociating character. The interference of the direct transition amplitudes to the continua, and those through the var ious overlapping predissociating resonances, gives rise to a resultant stru cture in the dissociation probability with the variation of omega(2). The b ound levels used are either (a) a group of three closely spaced vibrational -rotational levels. H (H) over bar 1 Sigma(g)(+) (upsilon = 4, j = 0 and 2) , J (1)Delta(g) (upsilon = 4, j = 2); and (b) the next group of three close ly spaced levels, H (H) over bar (1)Sigma(g)(+) (upsilon = 5, j = 0 and 2), J (1)Delta(g) (upsilon = 5, j = 2). Far from resonance with any predissoci ating level, the dissociation probability becomes equal to the value obtain ed by considering only the direct transitions to the continua. For differen t fixed values of omega(1), the variation of the dissociation probability a gainst omega(2) reflects the characteristics of the excitation of the inter mediate resonances with mixed B and C character. On or near resonance, the excitation of the predissociating levels of the J electronic state plays a crucial role in determining the dissociation line shape, whereas the excita tion of the predissociating levels of the H (H) over bar electronic state d o not affect the dissociation line shape significantly. [S1050-2947(99)0320 8-4].