Contribution of the Breakdown of the Born-Oppenheimer Approximation to Higher Order Dunham Coefficients.

By means of a Deltaomega and DeltaB formalism for correction parameters, expressions were derived for higher-order Dunham coefficients, YvJ04, YvJ12, and YvJ21, in which contributions of the breakdown of the Born-Oppenheimer approximation were taken into account. Including YvJ04, YvJ12, and YvJ21, and Dunham's Y09, Y17, and Y25 coefficients in addition to the lower-order Y*vJij and Yk1 in the analysis, an extensive data set of the vibrational-rotational and the rotational transitions for four isotopomers of lithium hydride was fitted simultaneously to a single set of molecular constants within experimental errors. Since lithium hydride is a very light molecule, expressions shown in the present article should provide a means applicable to most cases of the spectral analysis of diatomic molecules in the 1Sigma state. Copyright 1998 Academic Press.