TRANSITION MOMENT VARIATION IN THE $A^{2} \Sigma \rightarrow X^{2} \Pi$ TRANSITION OF HYDROGEN HALIDES

The relative emission intensity of vibrational bands due to the $A^{2} \\Sigma \\rightarrow X^{2} \\Pi$ transition in $HCl^{+}$, $DCl^{+}$ and $HBr^{+}$ have been measured. The intensities of bands in a progression from a fixed upper state were compared with the Franck-Condon factors. The observed intensities became increasingly smaller than the Franck-Condon factors predicted as $v^{\\prime\\prime}$ increased in each progression. The results were interpreted as a decrease in the transition moment with increasing internuclear separation. When treated in this fashion $DCl^{+}$ gives the same quautitative decrease as $HCl^{+}$. The intensity variation can be fit by using a power series expansion in the internuclear separation for the electric dipole moment.