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 SiF 4 /M = 1/6000-1/10 000 in an N 2 matrix at 11 K (for comparison, the spectra of SiF 4 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 ν 3 band of the SiF 4 ( 28 SiF, 29 SiF 4 , and 30 SiF 4 ) isotopologues of the SiF 4 molecule and in the range of the ν 1 + ν 4 , ν 2 + ν 3 , and ν 1 + ν 3 bands of 28 SiF 4 , whereas, in the range of the 2ν 3 band of 28 SiF, a triplet appears. In order to analyze the influence of the matrix on the spectrum of free SiF 4 molecules, we have used a model that makes it possible to successively calculate (i) the spectrum of SiF 4 in terms of the model of local modes, (ii) the structure of a matrix composed by 864 N 2 molecules + a rigid SiF 4 molecule using the Monte Carlo method, and (iii) the interaction of matrix particles with local dipole moments in the approximation of dipoleinduced 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 SiF 4 molecules obeying the T d symmetry are realized in the nitrogen matrix.

Infrared Spectra and Structures of SiH4and GeH4Dimers in Low-Temperature Nitrogen Matrixes

“…After a number of displacements, the ensemble reached a stationary state in which its energy was minimal. The SiH 4 molecule occupies a vacant site from which one nitrogen molecule was removed from the nitrogen lattice …”

“…The calculations also show that, after rotation about the Z axis though 120°, the nitrogen molecules indicated by letters a , b , c , d replace each other to within an error not exceeding 0.1 Å (0.06 Å for the center of molecules). Note that, in the case of SiF 4 , at least three nitrogen molecules should be removed …”

“…We performed the calculations in terms of classical physics using the atom–atom potential, which allowed us to analyze the structure of many-particle systems. A cubic box containing 863 N 2 particles and a rigid nonmoving SiH 4 molecule located at the center of the box , was used in the calculation. After a number of displacements, the ensemble reached a stationary state in which its energy was minimal.…”

Infrared Studies of the Symmetry Changes of the 28SiH4 Molecule in Low-Temperature Matrixes. Fundamental, Combination, and Overtone Transitions

“…2 It should be mentioned that the appearance of additional bands and structure in the spectra can also be associated with the formation of weak van der Waals complexes, in particular, complexes characterized by resonant dipole−dipole (RDD) interactions. The formation probability of dimers, for example, (SF 6 ) 2 , 4−7 (SiF 4 ) 2 , 8,9 and others, 4 increases at low temperatures T < 10−15 K.…”