Vibrational spectra of adenine molecules in Kr, Ar, and Ne matrices

Abstract

IR Fourier spectra of adenine molecules isolated in low-temperature Kr, Ar, and Ne matrices are obtained over the frequency range of 3800–450 cm−1 with a resolution of 0.25 cm−1. MP2 and DFT/BeLYP quantum-mechanical calculations are used to determine the populations of the main structural isomers of adenine for different evaporation temperatures. It is found that the populations of the minor isomers of adenine do not exceed the observation threshold of 0.2% at an evaporation temperature of 450 K. The effect of the matrices reduces to splitting most of the absorption bands of the main isomer A_9H. Splitting of a number of deformation vibration bands owing to Fermi resonances is observed in the 1700–450 cm−1 range. DFT/B3LYP calculations with a polynomial correction for the frequencies of the vibrational spectra are used to determine the spectral ranges within which it is best to search for the most intense vibrations of the rare isomers: 3440–3310, 1710–1680, and 1580–1540 cm−1. It is found that a triple Fermi resonance occurs for γN9H out-of-plane vibrations with participation of librational modes.