Electronic Structure and Kinetics Calculations for the Si+SH Reaction, a Possible Route of SiS Formation in Star-Forming Regions

Quasiclassical Trajectory Study of the Si + SH Reaction on an Accurate Double Many-Body Expansion Potential Energy Surface

“…The reported value of 8.6 × 10 –10 cm 3 s –1 for 200 K was found, with a positive temperature dependence. De Castro et al studied the Si + SH­( v = 0, j = 1) reaction based on a many-body expansion potential energy surface (PES) calibrated from multireference configuration interaction (MRCI) energies after extrapolation to the complete basis set (CBS) limit. , Using the latter, they reported a specific thermal rate constant of 5.5 × 10 –14 cm 3 s –1 for T ≤ 500 K, i.e., nearly 5 orders of magnitude smaller than the value reported by Rosi et al Most recently, we showed that the title reaction is very relevant for the SiS formation, but conversely to Rosi et al, the thermal rate coefficient was found to decrease with temperature and showed a value nearly 1 order of magnitude smaller. Indeed, the use of such smaller values in an astrochemical model of a shock region similar to L1157-B1 led to values that match the observed ones …”

“…As in previous work, the SiSH* complex was assumed to be formed when the potential energy was 10% lower than the energy of TS2 diss . The inset of Figure 7 shows the nonstatistical recrossing, opposite to the statistical that arises from transition state theory, calculated as the quotient of the number of reactive 17 studied the title reaction using a Langevin-type capture model for the Si + SH → SiSH association reaction and calculated the unimolecular decomposition step using RRKM theory. For the energetic description of the process, they employed DFT with the B3LYP functional and the aug-cc-pV(T +d)Z basis set.…”

“…In the first case, they fitted the long-range potential to a −C 6 r −6 function, which is very similar to the results here reported for the spherically averaged potential (n = 6.29). It should be emphasized that the topography of the potential energy surface along the reaction path may have a major effect on the recrossing, which was not taken into account by Rosi et al, 17 while the use of transition state theory does not follow from the topography of the global potential energy surface.…”

“…For astrochemical modeling, it is necessary to have accurate rate constants for the involved reactions. Although the rate coefficients currently available in the KIDA and UMIST databases involving this species are related to reactions involving ions, there has been a recent effort to investigate neutral–neutral processes for its formation and destruction both computationally − and experimentally . Rosi et al recently reported rate constants for the Si + SH reaction based on a Langevin-type capture model and the Rice–Ramsperge–Kassel–Marcus (RRKM) unimolecular reaction.…”

“…Although the rate coefficients currently available in the KIDA and UMIST databases involving this species are related to reactions involving ions, there has been a recent effort to investigate neutral–neutral processes for its formation and destruction both computationally − and experimentally . Rosi et al recently reported rate constants for the Si + SH reaction based on a Langevin-type capture model and the Rice–Ramsperge–Kassel–Marcus (RRKM) unimolecular reaction. Using density functional theory (DFT) and the coupled-cluster method including single and double electronic excitations and a perturbative correction for triples (CCSD­(T)), they characterized the reaction pathways on the doublet state of SiSH using the aug-cc-pV­( T + d )­Z Dunning-type basis set , and calculating the harmonic vibrational frequencies with DFT using the B3LYP functional .…”