Matrix site effects on vibrational frequencies of HXeCCH, HXeBr, and HXeI: a hybrid quantum-classical simulation.

Keisuke Niimi,Tetsuya Taketsugu,Akira Nakayama

doi:10.1039/c5cp00568j

Abstract

The matrix shifts of the H-Xe stretching frequency of noble-gas hydrides, HXeCCH, HXeBr, and HXeI in various noble-gas matrices (in Ne, Ar, Kr, and Xe matrices) are investigated via the hybrid quantum-classical simulations. The order of the H-Xe stretching frequencies is found to be ν(gas) < ν(Ne) < ν(Xe) < ν(Kr) < ν(Ar) for HXeCCH and HXeBr, while it is ν(gas) < ν(Ne) < ν(Xe) < ν(Ar) < ν(Kr) for HXeI. This order is anomalous with respect to the matrix dielectric constants, and the calculated results reproduce the experimentally observed shifts quite successfully. We also find that the matrix shifts from the gas-phase values are Δν(HXeCCH) ≈ Δν(HXeCl) < Δν(HXeBr) < Δν(HXeI) in the same noble-gas matrix environments, which implies that the weakly bound molecules exhibit large matrix shifts. The local trapping site is analyzed in detail, and it is shown that a realistic modeling of the surrounding matrix environments is essential to describe the unusual matrix shifts accurately.

Highlights

The last two decades have witnessed a rebirth of interest in the field of noble-gas chemistry mainly due to the discovery of noblegas hydrides.[1,2,3,4,5,6,7] These compounds have the structural formula of HNgY, where Ng is a noble gas atom and Y is an electronegative fragment
The geometry optimizations were performed for HXeCCH, HXeBr, and HXeI using the CCSD(T) method, and the vibrational frequency analysis followed it
As already demonstrated in our previous work,[28] these results indicate that a more realistic modeling of the matrix environments is necessary for HXeCCH, HXeBr, and HXeI

Summary

Introduction

The last two decades have witnessed a rebirth of interest in the field of noble-gas chemistry mainly due to the discovery of noblegas hydrides.[1,2,3,4,5,6,7] These compounds have the structural formula of HNgY, where Ng is a noble gas atom and Y is an electronegative fragment. The vibrational frequencies of single-layer calculations by Ne atoms were strongly red-shifted from that of the isolated HXeCl; the shifts were À50 cmÀ1 and À192 cmÀ1 for harmonic and anharmonic calculations, respectively, which are the largest among the single-layer cages of four Ng atoms (Ng = Ne, Ar, Kr, and Xe) This is in contrast to the general observations that the interaction of an embedded compound with Ne atoms is the weakest and that the vibrational frequency in a Ne matrix should be closest to the situation in the gas phase.[27]. The largest shifts were predicted for the Ar matrix by our simulations and at that time we were not aware of the experimental results of the Ar matrix, but the very recent experimental results are in accord with our prediction.[19] It is noteworthy that the two different approaches of Kalinowski et al.[19] and ours predict the same order of vibrational frequency for HXeCl embedded in four noble-gas matrices. We performed the simulations for HXeI in Ar, Kr, and Xe matrices, and the calculated order is in accord with the experimental data.[31]

Computational details

Results and discussion

Hybrid quantum-classical simulations in the solid matrices

Conclusions and outlook