BOUND-BOUND AND BOUND-FREE FLUORESCENCE FROM THE $A^{1}\Sigma^{+}$ STATE TO THE $X^{1}\Sigma^{+}$ STATE IN LIH

Using experimentally-based potential energy $curves^{1}$ and a theoretical transition $moment^{2}$, we report calculated bound-bound and bound-continuum radiative transition probabilities for several high-lying v' levels of the $A^{1}\\Sigma^{+}$ state in LiH, We will interpret the broad oscillatory structures in the continuum region as well as the region of the threshold between the bound and continuum levels of the X state. Our calculations include proper, non-zero rotational dependence. We have recently observed fluorescence from $^{6}LiH, ^{7}LiH$ and $^{7}LiD$ excited by UV lines of an argon ion laser (3336, 3345 and $3358 \\AA$, respectively). The levels excited in the $A^{1}\\Sigma^{+}$ state for these three cases are (v', J') = (12, 10), (16, 9) and (19, 22), respectively, so significant bound-free emission is expected in addition to the bound-bound emission already observed. In the case of emission from the $A^{1}\\Sigma^{+} (v'=26, J'=0)$ long-range level to the $X^{1}\\Sigma^{+} (k", J"=1)$ levels, a very strong enhancement in the intensity occurs right at the threshold transition energy. This very narrow and extremely intense line is interpreted as due to existence of a quasibound level in line X state when J"=1.