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Chirped-pulse (CP) Fourier transform rotational spectroscopy is uniquely suited for near-universal quantitative detection and structural characterization of mixtures that contain multiple molecular and radical species. In this work, we employ CP spectroscopy to measure product branching and extract information about the reaction mechanism, guided by kinetic modeling. Pyrolysis of ethyl nitrite, CH[subscript 3]CH[subscript 2]ONO, is studied in a Chen type flash pyrolysis reactor at temperatures of 1000–1800 K. The branching between HNO, CH[subscript 2]O, and CH[subscript 3]CHO products is measured and compared to the kinetic models generated by the Reaction Mechanism Generator software. We find that roaming CH[subscript 3]CH[subscript 2]ONO → CH[subscript 3]CHO + HNO plays an important role in the thermal decomposition of ethyl nitrite, with its rate, at 1000 K, comparable to that of the radical elimination channel CH[subscript 3]CH[subscript 2]ONO → CH[subscript 3]CH[subscript 2]O + NO. HNO is a signature of roaming in this system., Donors of the American Chemical Society Petroleum Research Fund (Grant 50650-ND6), United States. Dept. of Energy. Office of Basic Energy Sciences (Award DEFG0287ER13671), United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001198), Swiss National Science Foundation (Postdoctoral Research Grant PBEZB2-140081)

Quantum effects play a crucial role in chemical reactions involving light atoms at low temperatures, especially when a light particle is exchanged between two heavier partners. Different theoretical methodologies have been developed in the last decades attempting to describe zero-point energy and tunneling effects without abandoning a classical or semiclassical framework. In this work, we have chosen the D + HMu → DMu + H reaction as a stress test system for three well-established methods: two representative versions of transition state theory (TST), canonical variational theory and semiclassical instanton, and ring polymer molecular dynamics (RPMD). These calculations will be compared with accurate quantum mechanical results. Despite its apparent simplicity, the exchange of the extremely light muonium atom (0.114 u) becomes a most challenging reaction for conventional methods. The main result of this work is that RPMD provides an overall better performance than TST-based methods for such a demanding reaction. RPMD might well turn out to be a useful tool beyond TST applicability., Spanish Ministry of Science and Innovation (Grant CTQ2012-37404-C02), Spanish Ministry of Science and Innovation (Grant Consolider Ingenio 2010 CSD2009-00038), United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001198)

The thermal rate constant of the O([superscript 3]P) + CH[subscript 4] → OH + CH[subscript 3] reaction is investigated with ring polymer molecular dynamics on a full-dimensional potential energy surface. Good agreement with experimental and full-dimensional quantum multiconfiguration time-dependent Hartree results between 300 and 1500 K was obtained. It is shown that quantum effects, for example, tunneling and zero-point energy, can be effectively and efficiently included in this path-integral based approach implemented with classical trajectories. Convergence with respect to the number of beads is rapid, suggesting wide applicability for other reactions involving polyatomic molecules., United States. Dept. of Energy (DE-FG02-98ER14914), United States. Dept. of Energy. Office of Basic Energy Sciences (Combustion Energy Research Fellowship Award DE-SC0001198)

Using a recently developed full-dimensional accurate analytical potential energy surface [Gonzalez-Lavado, E., Corchado, J. C., and Espinosa-Garcia, J. J. Chem. Phys. 2014, 140, 064310], we investigate the thermal rate coefficients of the O([superscript 3]P) + CH[subscript 4]/CD[subscript 4] reactions with ring polymer molecular dynamics (RPMD) and with variational transition-state theory with multidimensional tunneling corrections (VTST/MT). The results of the present calculations are compared with available experimental data for a wide temperature range 200–2500 K. In the classical high-temperature limit, the RPMD results match perfectly the experimental data, whereas VTST results are smaller by a factor of 2. We suggest that this discrepancy is due to the harmonic approximation used in the present VTST calculations, which leads to an overestimation of the variational effects. At low temperatures the tunneling plays an important role, which is captured by both methods, although they both overestimate the experimental values. The analysis of the kinetic isotope effects shows a discrepancy between both approaches, with the VTST values smaller by a factor about 2 at very low temperatures. Unfortunately, no experimental results are available to shed any light on this comparison, which keeps it as an open question., Gobierno de Extremadura, Spain, La Federacion Espanola de Enfermedades Raras (Project IB10001), United States. Dept. of Energy. Office of Basic Energy Sciences (Combustion Energy Research Center Award DE-SC0001198)