Structures of vibrational absorption bands of the SiF4 molecule in a low-temperature nitrogen matrix

Abstract

We have studied the IR absorption spectra of diluted mixtures SiF4/M = 1/6000–1/10 000 in an N2 matrix at 11 K (for comparison, the spectra of SiF4 in Ar and Xe matrices have also been studied). It has been shown that, in solid nitrogen, the appearance of doublets is observed both in the range of the ν3 band of the SiF4 (28SiF, 29SiF4, and 30SiF4) isotopologues of the SiF4 molecule and in the range of the ν1 + ν4, ν2 + ν3, and ν1 + ν3 bands of 28SiF4, whereas, in the range of the 2ν3 band of 28SiF, a triplet appears. In order to analyze the influence of the matrix on the spectrum of free SiF4 molecules, we have used a model that makes it possible to successively calculate (i) the spectrum of SiF4 in terms of the model of local modes, (ii) the structure of a matrix composed by 864 N2 molecules + a rigid SiF4 molecule using the Monte Carlo method, and (iii) the interaction of matrix particles with local dipole moments in the approximation of dipole-induced dipole and dipole-quadrupole interactions. The model describes satisfactorily the low-frequency shift of bands in the nitrogen matrix. All obtained experimental and theoretical results are consistent with the assumption that two kinds of stable trapping centers of SiF4 molecules obeying the Td symmetry are realized in the nitrogen matrix.