Infrared Spectra and Intermolecular Potentials of Matrix‐Isolated Nitromethane and Nitromethane‐d3

The infrared spectra of protonated and deuterated nitromethane isolated in a nitrogen matrix have been recorded from 4000 to 250 cm−1. Peaks have been assigned to monomer and dimer species by varying the concentration of nitromethane in the matrix. The frequencies of the monomer have been used in a normal coordinate analysis and the force constants evaluated agree well with those of the gas phase. The Cartesian displacements of the atoms for each normal mode are reported. These displacements showed that for the ``NO2 antisymmetric vibration'' there was considerably more motion of the hydrogen atoms. Lennard‐Jones‐type potentials were used to calculate dimer configurations with a minimum intermolecular potential energy, taking into account both dispersion and electrostatic forces. The charges on the atoms needed for the calculation of electrostatic forces were calculated from molecular orbital theory using both the MWH method and the INDO method. The position of minimum potential energy is a function of di...