Observation of organosulfur products (thiovinoxy, thioketene and thioformyl) in crossed-beam experiments and low temperature rate coefficients for the reaction S(1D) + C2H4

Abstract

The reaction between excited sulfur atoms, S(¹D), and the simplest alkene molecule, ethene, has been investigated in a complementary fashion in (a) crossed-beam dynamic experiments with mass spectrometric detection and time-of-flight (TOF) analysis at a collision energy of 37.0 kJ mol⁻¹, (b) low temperature kinetic experiments ranging from room temperature down to 23 K, and (c) electronic structure calculations of stationary points and product energetics on the C₂H₄S singlet potential energy surface. The rate coefficients for total loss of S(¹D) are found to be very large (ca. 4 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹) down to very low temperature indicating that the overall reaction is barrier-less. From laboratory angular and TOF distributions at different product masses, three competing reaction channels leading to H + CH₂CHS (thiovinoxy), H₂ + CH₂CS (thioketene), and CH₃ + HCS (thioformyl) have been unambiguously identified and their dynamics characterized. Branching ratios have also been estimated. These studies, which exploit the capability of producing intense supersonic beams of sulfur S(³P,¹D) atoms and measuring rate coefficients down to very low temperature, offer considerable promise for further dynamical investigations of other sulfur atom reactions of particular relevance to combustion and atmospheric chemistry.