Theoretical Study of the SC₃H_m⁺Systems,m= {3, 4}

Abstract

A comprehensive theoretical study of the potential energy surfaces of the lowest-lying doublet and quartet electronic states of the SC 3 H 4 + system has been performed by means of a combination of density functional and ab intio methods. The potential energy surfaces corresponding to the lowest doublet and quartet electronic states have turned out to be extremely complex. Twenty-six doublet species and twenty-four quartet species have been identified, some of them having several stable conformations. The quartet states are normally much higher in energy than the doublet states. The absolute minimum is the methylthioketene cation, but the 2H-thiete cation, the thioacrolein cation, and the methylthiirene cation lie very close in energy; all of them are doublet states. The most stable quartet species is the thioxyallyl cation. In addition, a rather detailed analysis of the fragmentation of this system has been made. All of the products that are obtained in the S + + CH 3 CCH reaction, which is an important step in the generation of sulfur-containing cumulenes of astrophysical significance, have been included in this analysis, namely, a number of states of the SC 3 H 3 + , HCS + , C 3 H 3 + , C 2 H 3 , and C 3 H 4 + systems. Special attention has been paid to the SC 3 H 3 + system. In addition, the interaction between S + and CH 3 CCH through a number of electronic states has been studied by means of a multireference configuration interaction approach. The results suggest that an intersystem crossing process leading to the doublet potential energy surface of the SC 3 H 4 + system may play a key role. Some potentially crucial reaction mechanisms have been proposed.

Reactions of F+(3P) and F+(1D) with Silicon Oxide. Possibility of Spin-Forbidden Processes

“…Gas-phase ion processes are of great relevance in atmospheric and interstellar chemistry. − It is nowadays well established that ion−molecule reactions seem to be in the origin of the different species detected inside interstellar clouds. , However, in general, the only information available in most of these processes is the product distribution, but very little is known about the mechanism leading to these products. − In this respect the role of high-level ab initio molecular orbital techniques − was of great importance in elucidating these mechanisms. − Actually, in many occasions, the ab initio or density functional theory calculations are the only alternative available to investigate the structures of ionic species, which, very often, are elusive to experimental observation. Besides, high-level theoretical methods reach the so-called chemical accuracy , and therefore, many thermodynamic properties of neutral and charged species can be estimated within ±2.0 kcal/mol of the experimental values, when available. − High accuracy is important in this field because in interstellar space only exothermic processes are likely to occur, due to the extreme interstellar conditions of low temperature and density, and therefore an accurate knowledge of the topology of the corresponding potential energy surface (PES) is of critical importance.…”