Barrierless reactions between two closed-shell molecules. II. Dynamics of F2+CH3SSCH3 reaction

Abstract

A second example of a barrierless reaction between two closed-shell molecules is reported. The reaction F(2)+CH(3)SSCH(3) has been investigated with crossed molecular beam experiments and ab initio calculations. Compared with previous results of the F(2)+CH(3)SCH(3) reaction [J. Chem. Phys. 127, 101101 (2007); J. Chem. Phys. 128, 104317 (2008)], a new product channel leading to CH(3)SF+CH(3)SF is observed to be predominant in the title reaction, whereas the anticipated HF+C(2)H(5)S(2)F channel is not found. In addition, the F+C(2)H(6)S(2)F product channel, the analog to the F+C(2)H(6)SF channel in the F(2)+CH(3)SCH(3) reaction, opens up at collision energies higher than 4.3 kcal/mol. Angular and translational energy distributions of the products are reported and collision energy dependences of the reaction cross section and product branching ratio are shown. The reaction barrier is found to be negligible (<<1 kcal/mol). Multireference ab initio calculations suggest a reaction mechanism involving a short-lived intermediate which can be formed without activation energy.

Multireference Electron Correlation Methods: Journeys along Potential Energy Surfaces

“…Pyrrole was also used as an example to demonstrate geometry optimization with XMS-CASPT2 . Single-state CASPT2 optimizations (including ground and excited states) have been shown to perform well for bond formation/breaking or energy transfer problems for a variety of chemical systems. − Furthermore, CASPT2 geometries are often used to benchmark other computational methods, including those generated under extreme conditions or not observed in experiment. , These studies include optimizations along the reaction pathway for the F 2 + CH 3 SCH 3 reaction; , ground-state optimization of the hydromethoxy radical; geometries and excitation energies for RPSB models for benchmarking the performance of CASSCF, CC2, MP2, and DFT; the potential energy landscape search of singlet fission material candidate tetracyanoquinodimethane bithiophene (QOT2); and the equilibrium geometry, frequency calculation, and reaction pathway for the ring-opening reaction of azaborine . The analytical nuclear gradient for FIC-CASPT2 has been used for the copper corrole complex (Figure ), where a saddled geometry was obtained for the S 0 state while the S 1 state is planar.…”

“…311−313 Furthermore, CASPT2 geometries are often used to benchmark other computational methods, including those generated under extreme conditions or not observed in experiment. 314,315 These studies include optimizations along the reaction pathway for the F 2 + CH 3 SCH 3 reaction; 311,312 groundstate optimization of the hydromethoxy radical; 315 geometries and excitation energies for RPSB models for benchmarking the performance of CASSCF, CC2, MP2, and DFT; 316 the potential energy landscape search of singlet fission material candidate tetracyanoquinodimethane bithiophene (QOT2); 313 and the equilibrium geometry, frequency calculation, and reaction pathway for the ring-opening reaction of azaborine. 314 The analytical nuclear gradient for FIC-CASPT2 has been used for the copper corrole complex (Figure 4), 203 where a saddled geometry was obtained for the S 0 state while the S 1 state is planar.…”

Kinetics and Products of the Reactions of F2 with Br‐Atom and Br2

“…So, on the one hand, molecular fluorine manifests relatively high reactivity with respect to some closed‐shell molecules and, on the other hand, it relatively slowly reacts with chemically active species, such as halogen and oxygen atoms. It was demonstrated, for example, that reactions of F 2 with organosulfur compounds, CH 3 SCH 3 and CH 3 SSCH 3 , and with limonene are barrierless reactions . Unexpectedly high (for reaction between two closed‐shell molecules) value, 1.6 × 10 −11 cm 3 molecule −1 s −1 at 298 K, was reported for the rate constant of the reaction of F 2 with CH 3 SCH 3 .…”

Reaction of Limonene with F2: Rate Coefficient and Products

“…In this respect, the F 2 molecule, manifesting relatively high reactivity with respect to some stable molecules, seems to be an exception of the rule. For example, crossed molecular beam experiments supported by ab initio calculations have demonstrated that reactions of molecular fluorine with organosulfur compounds, DMS (CH 2 SCH 3 ) and DMDS (CH 3 SSCH 3 ), are barrierless reactions. − An unexpectedly high value, 1.6 × 10 –11 cm 3 molecule –1 s –1 at 298 K, was reported for the rate constant of the reaction of F 2 with DMS …”