VIBRONIC EXCITATION IN $Na^{*} + Na_{2}$ COLLISIONS

[1] L. K. Lam, T. Fujimoto, A. C. Gallagher and M. M. Hessel: J. Chem. Phys., 68, 3553 (1978).Author Institution:The system $Na/Na^{*}/Na_{2}/Na^{*}_{2}$ is encountered in alkali vapor lasers and sodium discharge lamps. Depending on the pressures of the constituents the overall process $Na^{*} + Na_{2}^{*} \rightarrow Na+Na_{2}^{*}$ may occur radiatively or collisonally [1]. We have modelled experimental data taken from [1], as well as data obtained in this laboratory, in order to elucidate (a) the relative contributions from radiative and collisional transfer and, more important, (b) the pattern of vibrational excitation in the $Na_{2}^{*}$ (A) state consequent on collisional transfer between $Na^{*}$ and $Na_{2}$. So far as we are aware this is the first data on the latter point. Using a variety of models (the Golden Rule, ion-pair intermediates, the impulsive model, collision-complex) we have attempted to simulate the $Na_{2}$ fluorescence spectrum recorded under conditions where collisional energy-transfer, $E\rightarrow $E,V, dominated [1]. In order to fit this spectrum we find we must invoke collisional transfer dynamics of a type which has been observed previously in some cases of pure $E\rightarrow V$ transfer (rather than $E\rightarrow E,V$); in part the $Na_{2}$ is excited resonantly to high v` -levels of $Na_{2}^{*}$(A), and in part non-resonantly to low v` -levels