By means of a Delta(w), and Delta(B) formalism for correction parameters, expressions were derived for higher-order Dunham coefficients, Y-04*(upsilon J), Y-12*(upsilon J), and Y (21)*(upsilon J), in which contributions of the breakdown of the Born-Oppenheimer approximation were taken into account. Including Y (04)*(upsilon J), Y (12)*(upsilon J) and 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 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 (1) Sigma state. (C) 1998 Academic Press.