Dynamics of Ring Cleavage and Substitution in the Reactive Scattering of O(³P) Atoms with C₂H₄S and C₄H₄S Molecules

Abstract

Reactive scattering of ground state O( 3 P) atoms with C 2 H 4 S and C 4 H 4 S molecules has been studied at an initial translational energy E ∼ 40 kJ mol -1 using a supersonic beam of O atoms seeded in He buffer gas generated from a microwave discharge source. The center-of-mass angular distribution of SO scattering for O + C 2 H 4 S is cone-shaped in the backward hemisphere at a scattering angle θ ∼ 120°with respect to the incident O atom direction, while the OC 4 H 3 S scattering for O + C 4 H 4 S is nominally isotropic. The O + C 2 H 4 S reaction disposes a lower fraction (f ′ ∼ 0.3) of the total available energy into product translation than the O + C 4 H 4 S reaction (f ′ ∼ 0.4), although the product translational energies are higher by a factor of ∼2 for the more exoergic O + C 2 H 4 S reaction. The O + C 2 H 4 S reaction involves cleavage of the three-membered ring of the thiirane molecule, while the O + C 4 H 4 S reaction involves H atom displacement from the fivemembered ring of the thiophene molecule. Both reactions occur on the triplet potential energy surface. The strongly exoergic concerted rupture of the three-membered thiirane ring disposes half the available energy into vibrational excitation of the ethene product molecule compared with only a fraction (∼0.13) being disposed into SO product vibration. The displacement reaction of the five-membered thiophene ring involves O atom addition forming a persistent OC 4 H 4 S complex with a potential energy barrier to H atom displacement.

Gaussian-2 theoretical and direct ab initio molecular dynamics study of the reaction of O(3P) with thiirane, O(3P)+C2H4S(1A1)→SO(3Σ-)+C2H4(1Ag)

“…) ; coworkers Ðnds little evidence of intersystem crossing. 7 In the direct MD study, a modest number of well-chosen trajectories was selected to visualize the key dynamic features of the reaction, particularly the formation and decay of the reaction intermediates and transition states. At the outset of a trajectory calculation, the internal state of the thiirane molecule is given by the vibrational and rotational quantum levels.…”

“…That is consistent with the highly anisotropic angular distributions observed in the experiment of Grice and coworkers. 7 When O(3P) makes an edge-on approach to an SÈC bond of thiirane parallel to the CÈC bond with a larger kinetic energy, the Ðrst SÈC bond rupture starts as the OS distance closes to B1.8È2.0 followed almost simultaneously by the A , second SÈC bond rupture. The simulated reactive collision, illustrated in Fig.…”

Continuous process of the vacuum ultraviolet- (VUV-) photochemical oxidation of thiophene in the gas phase

“…For the gas phase reaction of O with TP, a rate constant k O/TP = 1.2 × 10 −11 cm 3 molecule −1 s −1 was reported, 34,35 and, based on hypotheses published in the latter reference, it may be assumed that O might insert into the α-C-H bond (reaction (5), Scheme 1) or add to one of the free electron pairs of S (reaction (6), Scheme 1). C-H bond insertion and addition to a CvC bond (reaction (7), Scheme 1) 36 with subsequent proton shift would lead to the same 3-and 5-thiolen-2-ones (3H-2thiophenone (2) and 5H-2-thiophenone (3), respectively, Scheme 1).…”

“…• Absorbing species O 2 : initiating oxidation of TP by O (reactions (3) and/or (4)) e.g., 20,34,35 • Absorbing species O 2 : initiating oxidation of TP by O 3 , 33,54 • Absorbing species TP: oxidation by addition of O 2 to intermediate radicals generated by the photolysis of TP (reaction (13)), 27 • Absorbing species H 2 O: initiating oxidation of TP by HO • (reactions (11) and ( 12)). 39,55 Fig.…”

“…All three oxidants (O, O 3 and HO • ) also react with the S-function of TP [33][34][35]54,57 to form the corresponding sulfoxide (thiophene 1-oxide ( 15)) and sulfone (thiophene 1,1-dioxide ( 16), Scheme 4), the latter being assumed to eliminate SO 2 in the course of an oxidative degradation. SO 2 -analyses exhibit…”