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Matrix isolation infrared spectroscopy has been combined with theoretical calculations for the characterization of the 1:1 hydrogen-bonded complex between H2O and dimethyl methylphosphonate (DMMP). The symmetric O-H stretching mode was observed to shift 203 cm-1 to lower energy upon hydrogen bond formation, while a 32 cm-1 blue shift was noted for the H-O-H bending mode of the H2O subunit in the complex. These values compare extremely well with the (unscaled) shifts of -203 and +32 cm-1, respectively, that were calculated theoretically at the MP2/6-31+G** level. Additional perturbed modes of the DMMP subunit were observed, shifted relative to the parent band position. The greatest perturbation was to the P=O stretching mode near 1270 cm-1, where a shift of -17 cm-1 was observed (-21 cm-1 calculated theoretically). This suggests that the site of hydrogen bonding in the complex is at the P=O group, in agreement with theoretical calculations. The binding energy ΔE° for the 1:1 complex was calculated to be -7.7 kcal/mol.