Quantum and quasi-classical calculations for the S⁺ + H₂(v,j) → SH⁺(v′,j′) + H reactive collisions

Abstract

State-to-state cross sections for the S + + H 2 (v, j) → SH + (v′, j′) + H endothermic reaction are obtained with quantum wave packet(WP) and quasi-classical (QCT) methods for different initial rovibrational H 2 (v, j) over a wide range of translation energies. Final state distribution as a function of the initial quantum number is obtained and discussed. Additionally, the effect of the internal excitation of H 2 on the reactivity is carefully studied. It appears that energy transfer among modes is very inefficient, that vibrational energy is the most favorable for reaction and rotational excitation significantly enhance reactivity when vibrational energy is sufficient to reach the product. Special attention is also paid on an unusual discrepancy between classical and quantum dynamics for low rotational levels while agreement improves with rotational excitation of H 2 , An interesting resonant behaviour found in WP calculations is also discussed and is associated to the existence of roaming classical trajectories that enhance the reactivity of the title reaction. Finally, a comparison with the experimental results of Stowe et al. [1] for S + + HD and S + +D 2 reactions, finding a reasonably good agreement with those results. I IntroductionSulfur is one of the most abundant elements in space, after H, He, O, C and N. Its relative abundance with respect to H is 10 −5 . However, the relative abundance of all the sulfur containing molecules detected so far in space is several order of magnitudes lower. Sulfur has not being detected in ices in space, and it is therefore concluded that it must be present in highly refractive grains, not yet determined [2,3].The first step in the sulfur chemistry is the formation of its hydride, in neutral or cationic form. SH + can be formed in collisions of atomic S with , but ion is only abundant in cold molecular clouds. The recent detection of SH + in hot regions, such as star formation regions [4], diffuse clouds [5,6], and dense PDRs [7], indicates that there must by other routes * alexandre.zanchet@csic.es. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts to form this hydride cation. This low rotational N=1 → 0 transition of SH + ( 3 ∑ − ) was recently measured in the laboratory by Halfen and Ziurys [8].One possible pathway is the (1) reaction. This reaction is endothermic for H 2 (v = 0) by ≈ 0.86 eV [1,9], but it may be the source of SH + when considering vibrationally excited states of H 2 (v ≥ 2), as proposed by Agundez et al. [10].Very recently, a potential energy surface (PES) for the ground quartet electronic state of this system has been calculated, and reaction rate constants were obtained using a quasi-classical trajectory (QCT) method [11]. The rates obtained increase substantially with increasing the initial vibrational state of H 2 , and were used to model SH + fractional abundance as a function of the visual extinction, A v . For A v < 3, there is a notorious increase of the abundance of SH + because at t...

A global potential energy surface and time‐dependent quantum wave packet calculation of Au + H2 reaction

“…It indicates that the reaction is endothermic, and the endothermic energy is about 1.59 eV, which is lower than previous theoretical study [16] (1.66 eV). Besides, all the MEPs are exits a barrier, and heights are about 1.485 eV, 1.610 eV, 1.623 eV, and 1.593 eV, which are corresponding to 458, 908, 1208, and 1808, respectively.…”

“…and dr vv jv v0j0 ð#; EÞ dX The spectroscopic constants for the ground electronic states of AuH( 1 R 1 ) and H 2 (X 1 R g 1 ) molecule obtained from the new PES, compared with the experimental data [48] and Zanchet PES [16] R e (Å) D e (eV) x e (cm 21 ) [16] and the experimental data [52] are also listed in the Table 1. Spectroscopic constants of the diatomic molecules are calculated when the super molecule at a distance of 50 Å far from the other atom.…”

“…To intuitively compare with the Zanchet PES, [16] the global MEPs from the reactant channel Au 1 H2 to the product channel H 1 AuH channel of the two PESs are shown in the Figure 3. Besides, the asymptotic energy of Au 1 H 2 is set as zero in all these MEPs.…”

“…With the development of calculation method and computing technologies, the high-precision ab initio methods have been used to study simple examples, such as Au N 1 H 2 (N < 4). [14][15][16] Balasubramania and Liao [17] studied two low-lying electronic states of AuH 2 and optimized the ground state of AuH 2 using different methods in 1988. Using CASSCF/MRSDCI methods on the bending potential energy surface (PES) of AuH 2 , Balasubramanian et al [18] found the ground state of AuH 2 decomposition into Au( 2 S) 1 H 2 need to step over a barrier.…”

“…Zanchet et al [16] constructed a global PES (Zanchet PES) for the ground state of AuH 2 using multireference configuration interaction (MRCI) with one-electron Gaussian-type basis set ECP60MDF [20] for Au atom and augmented correlation-consistent polarization valence triple zeta (augcc-pVTZ) [21] basis set for H atom. Two thousand three hundred seventy-six ab initio points were employed to fit the PES using the GFIT3C procedure.…”