THE PREDISSOCIATION MECHANISM FOR ${^{2}}\\Sigma^{+}$ RYDBERG STATES OF CALCIUM MONOCHLORIDE

This talk summarizes experimental results from recent ion-dip spectroscopy studies of CaCl as well as previously unpublished optical-optical-double-resonance work with specific regard to predissociation processes of $^{2}\\Sigma^{+}$ Rydberg states in the low-$n^{\\ast} (n^{\\ast} < 7, IP-E \\sim 2500 cm^{-1})$ region. A single repulsive state (assigned as ${^{2}}\\Sigma^{+}$) was found to be responsible for all observed predissociations of $^{2}\\Sigma^{+}$ Rydberg states. The $n^{\\ast}$-dependent internuclear distances of the intersections between Rydberg and repulsive $^{2}\\Sigma^{+}$ states were determined through the use of trial-and-error Franck-Condon calculations. Values of the $n^{\\ast}$-scaled electronic matrix elements governing the Rydberg $\\leftrightarrow$ repulsive state interaction were obtained from the measured linewidths $(.6 < \\Gamma < 1.2 cm^{-1})$ and computed Franck-Condon densities. With the assumption of a one-parameter form for the repulsive curve. $E(cm^{-1})=\\frac{C_{***}}{R^{***}}+D_{e},$ where $C_{12}$ has the units ${\\AA} {^{12}}cm^{-1}$ and $D_{e} = 33171 cm^{-1}$ for CaCl, the optimum values of $C_{12}$ was found to be $2.354 \\times 10^{8} {\\AA} {^{12}}cm^{-1}$.