Inelastic Neutron Scattering and Far IR Spectroscopy of Acetonitrile in Solid Ar and CCl₄ Matrices

Abstract

Clusters j Matrix Isolation j Molecular Interactions / Neutron Scattering j Spectroscopy, InfraredInelastic neutron scattering has been applied for the first time to the study of matrix isolated species whose thermodynamically stable phase under normal conditions is the liquid. The aims of these investigations, which are complemented by far infrared studies, are to explore the aggregational behaviour of acetonitrile and the intermolecular dynamics of the respective aggregates in low temperature matrices of solid Ar and CC4. The only aggregate observed, using a variety of different spectroscopic techniques and diverse experimental conditions, is an antiparallel dimer. In contrast to the external intermolecular modes of this aggregate, which were not accessible by vibrational spectroscopy, the internal modes could be described and assigned.

Gas-phase deposition of acetonitrile: an attempt to understand Ostwald’s step rule on a molecular basis

“…1) is formed in solid Ar matrix. The same observations were made for Kr [2] and CCl 4 [1] matrices. Owing to the symmetry selection rules, only two out of the totally 6 intermolecular modes are IR-active and give rise to absorption bands around 120 and 100 cm À1 (Fig.…”

“…Thus, the gas-phase deposited solid acetonitrile sample is likely to be an amorphous phase consisting of randomly oriented antiparallel dimers. 1 On slightly annealing there is an irreversible phase transformation evidenced by the appearance of a new complicated far IR spectrum (5-7 bands) [1] instead of the simple one related to the antiparallel dimer species. The conclusions presented are in agreement with Raman data obtained on solid acetonitrile samples [4,6].…”

“…The motivation for the present study stems from vibrational spectroscopic investigations aiming at the intermolecular interactions in aggregates of strongly polar acetonitrile molecules [1]. Far infrared spectroscopy clearly shows that only one type of aggregate, namely the antiparallel dimer (point group C 2h , Fig.…”

“…Unexpectedly, gas-phase deposition of pure acetonitrile at a temperature of 100 K or less and a deposition rate of 2.5 lmol min À1 or less gives rise to solid acetonitrile exhibiting a far IR spectrum which strongly resembles that of matrix isolated antiparallel dimers [1] ( Fig. 1).…”

Ab initio calculations of the structural, energetic, and vibrational properties of some hydrogen bonded and van der Waals dimers. Part 4. The acetonitrile dimer

“…The acetonitrile dimer has been the subject of a variety of previous studies, both theoretical 13–22 and experimental 23–35. The computational studies have used a number of theoretical models, varying from complete neglect of differential overlap (CNDO)/force 14, through restricted Hartree–Fock 13, 15, 16, 18, 19, 21, 22 and density functional theory (B3LYP) 22 to second‐ and fourth‐order Møller–Plesset perturbation theory (MP2 16–22 and MP4 22), and with basis sets ranging in size from 3‐21G 15, 16 to 6‐311++G(2d,2p) 22.…”