Crossed-Beam Dynamics, Low-Temperature Kinetics, and Theoretical Studies of the Reaction S(1D) + C2H4

The reaction between sulfur atoms in the first electronically excited state, S(1D), and ethene (C2H4) has been investigated in a complementary fashion in (a) crossed-beam dynamic experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (37.0 and 45.0 kJ mol−1), (b) low temperature kinetics experiments ranging from 298 K down to 23 K, and (c) electronic structure calculations of stationary points and product energetics on the C2H4S singlet and triplet potential energy surfaces. 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 temperatures indicating that the overall reaction is barrierless. 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. Product branching ratios have also been estimated. Interpretation of the experimental results on the reaction kinetics and dynamics is assisted by high-level theoretical calculations on the C2H4S singlet potential energy surface. RRKM (Rice−Ramsperger−Kassel−Marcus) estimates of the product branching ratios using the newly developed singlet potential energy surface have also been performed and compared with the experimental determinations.