Relative probabilities of spontaneous transitions in v '' progressions of the G(1)Sigma(+)(g),v ' -> B1 Sigma(+)(u),v '' bands of the H-2 molecule

The probabilities of spontaneous transitions in v" progressions of the G(1) Sigma(g)(+) --> B(1)Sigma(u)(+) bands of the H-2 molecule (the 3D --> 2B el ectronic transition in notations of G.H. Dieke) are, for the first time, ex perimentally studied. The line strength ratios were measured for 78 G(1)Sig ma(g)(+), v', J' --> B(1)Sigma(u)(+), v", J" electronic-vibrational-rotatio nal spectral lines having a common upper level but belonging to different b ands of v" progressions (the vibrational branching coefficients). For this purpose, the intensities of lines of the P and R branches, emitted by a low -pressure plasma and corresponding to different values of the rotational (J ' = 0-11) and vibrational (v' = 0-3 and v" = 0-7) quantum numbers, were use d. It was found that the changes in the vibrational branching coefficients with variation of v' and v' are significant (up to a factor of 20). For mos t bands studied, the dependences of the vibrational branching coefficients on the rotational quantum number J' of an upper level are rather weak and d o not exceed 30%. It was established that the difference between the experi mental values of ratios of the vibronic transition probabilities (summed ov er J') and the results of calculation in the adiabatic approximation strong ly depends on v', reaching a factor of 25 for a transition from the v' = 2 level. At the same time, the discrepancy between the experimental data and the results of nonadiabatic ab initio calculations lies between 1.0 and 2.3 . (C) 2000 MAIK "Nauka/Interperiodica".