POTENTIAL ENERGY CURVES OF THE $A ^{1}\Sigma$ STATES OF AgH AND CuH

Abstract

Some years ago $Learner^{a}$ recorded electronic spectra involving the $A ^{1}\Sigma^{+}$ state of AgH, and found anomalous behaviour of the vibrational level spacings and $B_{v}$ values which he attributed to the potential energy curve for this state having a ``shelf''. More recently, Witek $et al.^{b}$ reported ab initio results which supported Learner's assertion that the potential energy function for this state had an unusual shape, but found that rather than have a shelf, there was an abrupt stiffening of the bond for vibrational levels above $v \approx 4$. In order to clarify this situation, we have combined new and previously recorded visible $A - X$ spectra and high quality microwave and infrared data for $^{107/109} AgH$ and $^{107/109}AgD$ in a combined-isotopomer direct-potential-fit analysis which determines analytic potential energy and Born-Oppenheimer breakdown functions for this state. A similar approach is used to study the analogous $A ^{1}\Sigma^{+}$ state of $^{63/65}CuH$ and $^{63/65}CuD$.