An ab initio study of anharmonicity and field effects in hydrogen-bonded complexes of the deuterated analogues of HCl and HBr with NH3 and N(CH3)(3)

One- and two-dimensional nuclear Schrodinger equations have been solved on MP2/aug'-cc-pVDZ potential energy surfaces generated for ClH:NH3 and ClH:N( CH3)(3) and on MP2/6-31+G(d,p) surfaces generated for BrH:NH3 and BrH:N(CH3 )(3) to investigate deuterium substituent effects on the expectation values of X-N and X-H distances and on anharmonic dimer- and proton-stretching fr equencies. These studies have been carried out on all isotopomers in the pr esence of electric fields of varying strengths. Deuteration of HX or ammoni a or trimethylamine has only minor effects on expectation values and dimer- stretching frequencies. While deuteration of the nitrogen base also has onl y a minor effect on proton-stretching frequencies, deuteration of the hydro gen halide has a major effect, as expected. X-D stretching frequencies are always lower than the corresponding X-H frequencies at all field strengths, although the ratio nu (D)/nu (H) for corresponding pairs of isotopomers ma y be less than, equal to, or greater than the harmonic ratio of 0.71. Struc tural and vibrational spectral changes as a function of field strength are similar for a given complex and each of its isotopomers. The agreement betw een computed proton-stretching frequencies and experimental frequencies sup ports the validity of this approach for modeling matrix effects on the stru ctures and vibrational spectra of hydrogen-bonded complexes. The computed r esults provide insight into the nature of the hydrogen bonds that stabilize these complexes in low-temperature matrixes.