Ab initio and DFT studies of the structure, stability and vibrational spectrum of the hydrogen-bonded (CH 3) 2O⋯HONO 2 complex

Abstract

The structure, stability and vibrational spectrum of the hydrogen-bonded complex between HONO 2 and (CH 3) 2O have been investigated using ab initio and DFT calculations. Full geometry optimization was made for the complex studied. The corrected values of the dissociation energy at the SCF and MP2 levels and B3LYP calculations are indicative of relatively strong OH⋯O hydrogen-bonded interaction. The changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding between HONO 2 and (CH 3) 2O have been estimated. It was established that the most sensitive to the complexation is the stretching O–H vibration from HONO 2. In agreement with the experiment its vibrational frequency in the complex is shifted to lower wavenumbers. The calculated frequency shift with the MP2/6-311++G(2d,2p) is −435 cm −1 and with the B3LYP/6-31G(d,p) calculations is −578 cm −1, while the experimentally measured shift is −952 cm −1. The magnitude of the frequency shift is indicative of relatively strong OH⋯O hydrogen-bonded interaction. The intensity of this vibration increases dramatically upon hydrogen bonding. The ab initio calculations at the MP2 level predict an increase up to 13 times and the B3LYP/6-31G(d,p) predicted increase is up to 11 times.