Noble gas matrix effects on the symmetric stretching transition structure of the XNgY noble gas molecules: Theoretical understanding the noble gas matrix stabilizing effects

In order to understand the thermal stability of an XNgY (where X and Y are an electronegative atom or fragment, and Ng is a noble gas atom) molecule in a noble gas matrix rather than in a gas-phase phase, it is unavoidable or necessary to model the matrix effects on the noble gas molecule. In order to model a noble gas matrix effects on the symmetric stretching transition structure of an XNgY molecule, at least up to now, it is hard not to use a single-reference method such as MP2(FC) to study the transition structure, which has considerable multi-reference character. For 22 noble gas molecules with the general formula XNgY, the symmetric stretching transition structure has been calculated at both the MP2 (corresponding to a gas-phase structure) and MP2/IEF-PCM (corresponding to a noble gas matrix-solvated structure) levels of theory. Fortunately, for all of the 22 molecules, the stretching transition state predicted by the MP2 is, at least qualitatively, correct, leading to the X + Ng + Y dissociation limit. Upon the matrix effect modeling, for all of the 22 molecules, the equilibrium structure was stabilized while the stretching transition structure was destabilized or less stabilized. As a consequence, the three-body dissociation (XNgY → X + Ng + Y) barrier was increased. In other words, the kinetic stability of an XNgY molecule will probably be larger in a solvated noble gas matrix than in a gas phase, if the dissociation reaction works through the three-body channel.