CONTRIBUTION OF THE BREAKDOWN OF THE BORN-OPPENHEIMER APPROXIMATION TO HIGHER-ORDER DUNHAM COEFFICIENTS

By means of a Delta(w), and Delta(B) formalism for correction paramete rs, expressions were derived for higher-order Dunham coefficients, Y-0 4(upsilon J), Y-12*(upsilon J), and Y (21)*(upsilon J), in which cont ributions of the breakdown of the Born-Oppenheimer approximation were taken into account. Including Y (04)(upsilon J), Y (12)*(upsilon J) a nd Y (21)(upsilon J), and Dunham's Y-09, Y-17, and Y-25 coefficients in addition to the lower-order Y (ij)(upsilon J) and Y-k1 in the anal ysis, an extensive data set of the vibrational-rotational and the rota tional transitions for four isotopomers of lithium hydride was fitted simultaneously to a single set of molecular constants within experimen tal errors. Since lithium hydride is a very light molecule, expression s shown in the present article should provide a means applicable to mo st cases of the spectral analysis of diatomic molecules in the (1) Sig ma state. (C) 1998 Academic Press.