Infrared spectra and intermolecular potentials of matrix isolated methyl nitrate and methyl- d3-nitrate
The infrared spectra of protonated and deuterated methyl nitrate isolated in a nitrogen matrix have been recorded from 4000 to 250 cm -1. Peaks have been assigned to monomers, pairs, and higher-ordered species by varying the concentration of methyl nitrate in the matrix and also by inducing diffusion of molecules in the matrix. Monomer frequencies were used to calculate the normal coordinates, force constants, and cartesian displacements. Configurations of a pair of methyl nitrate molecules were calculated using an approximate nonbonded atom-atom potential including both Lennard-Jones and electrostatic potentials. The position of minimum energy was established as a function of the distance between molecules as well as angular rotation of the two molecules with respect to one another. Calculations of exciton splittings and shifts for the pair configuration computed to be most stable were evaluated by two site exciton theory and compared to the assigned pair frequencies.