The effect of matrices on the low-temperature IR spectra of formic acid molecule isolated in inert gas crystals

The structure and vibrational spectra of inert gas clusters (Ne, Ar, Kr, Xe) with an isolated formic acid molecule were simulated using the DFT/M06-2X method, The influence of the matrix en-vironment on the vibrational spectra of formic acid was studied. The values of the matrix shifts of the vibrational frequencies pre-dicted in the calculations are in good agreement with the experi-mental values. It was found that the best agreement between the calculated and experimental shifts is observed for clusters with the minimal deformation energy of an inert gas crystal. In this case, the ratio of the volume of the molecule embedded in the matrix and the volume of substituted matrix gas atoms allows one to determine only the minimal possible size of the matrix site. A good agreement between the calculated and experimental values of the matrix shifts indicates the correspondence of the calculated approach to real experimental conditions.