THE D-X BAND SYSTEM OF CaH

Abstract

A many lined spectrum which can be attributed to hitherto unknown bands of the $D^{2}\Sigma^{+} -X^{2}\Sigma^{+}$ system of $CaH,^{1}$ has been observed in absorption using a King furnace, The spectra were obtained under conditions of high resolution with a 10 m grating spectrograph. Analysis shows that the levels of $D^{2}\Sigma^{+}$ are all strongly perturbed. We present a theoretical model which takes account of the close lying $B^{2}\Sigma^{+}$ and $E^{2}\pi$ states and which gives a qualitative explanation of the observed perturbations. An important feature of the interpretation is that the accepted vibrational frequency of $D^{2}\Sigma^{+}$ must be reduced by a factor of 2.