Quantum dynamics of the O(3P)+CH4→OH+CH3 reaction: An application of the rotating bond umbrella model and spectral transform subspace iteration

Motivated by a recent crossed-beam experiment on the title reaction reported by Pan and Liu [J. Chem. Phys. 140, 191101 (2014)], a detailed dynamics study was performed at three collision energies using quasiclassical trajectory (QCT) calculations based on a full-dimensional potential energy surface recently developed by our group (PES-2014). Although theory/experiment agreement is not yet quantitative, in general the theoretical results reproduce the experimental evidence: the vibrational branching ratio of OH(v = 1)/OH(v = 0) is ~0.8/0.2, excitation of the antisymmetric CH stretching mode in methane increases reactivity by factor 2.28-1.50, although an equivalent amount as translational energy is more efficient in promoting the reaction and, finally, product angular distribution shifts from backward in the CH4(ν = 0) ground-state to sideways when the antisymmetric CH stretching mode is excited. These results give confidence to the PES-2014 surface, depend on the quantization procedure used, are comparable with recent QCT calculations or improve previous theoretical studies using a different surface, and demonstrate the utility of the theory/experiment collaboration.

Section: Introductionsupporting

confidence: 86%

Quasiclassical trajectory study of the effect of antisymmetric stretch mode excitation on the O(3P) + CH4(ν3 = 1) → OH + CH3 reaction on an analytical potential energy surface. Comparison with experiment

Monge‐Palacios

Gonzalez-Lavado

Espinosa‐García

2014

“…[8][9][10][11]15,[20][21][22][23][24][25]35,[39][40][41][42][43][44] The most elaborate calculations included six to seven degrees of freedom explicitly. The most detailed results can be obtained when reactions involving only few atoms are studied in gas phase or molecular beams.…”

Section: Introductionmentioning

confidence: 99%

A transition state view on reactive scattering: Initial state-selected reaction probabilities for the H+CH4→H2+CH3 reaction studied in full dimensionality

Schiffel

Manthe

2010

Initial state-selected reaction probabilities for the H+CH(4)→H(2)+CH(3) reaction are computed for vanishing total angular momentum by full-dimensional calculations employing the multiconfigurational time-dependent Hartree approach. An ensemble of wave packets completely describing reactivity for total energies up to 0.58 eV is constructed in the transition state region by diagonalization of the thermal flux operator. These wave packets are then propagated into the reactant asymptotic region to obtain the initial state-selected reaction probabilities. Reaction probabilities for reactants in all rotational states of the vibrational 1A(1), 1F(2), and 1E levels of methane are presented. Vibrational excitation is found to decrease reactivity when reaction probabilities at equivalent total energies are compared but to increase reaction probabilities when the comparison is done at the basis of equivalent collision energies. Only a fraction of the initial vibrational energy can be utilized to promote the reaction. The effect of rotational excitation on the reactivity differs depending on the initial vibrational state of methane. For the 1A(1) and 1F(2) vibrational states of methane, rotational excitation decreases the reaction probability even when comparing reaction probabilities at equivalent collision energies. In contrast, rotational energy is even more efficient than translational energy in increasing the reaction probability when the reaction starts from the 1E vibrational state of methane. All findings can be explained employing a transition state based interpretation of the reaction process.

“…[12][13][14][15][16][17] There have also been studies on bend-excitation in the O + CH 4 reaction. [18][19][20] However, apart from very recent computational studies on the F + CH 4 ͑v 4 =1͒ and F + CH 2 D 2 ͑v 9 =1͒ reactions, 21,22 the previous work usually focused on the late-barrier polyatomic reactions ͑the transition state has a product-like structure͒ and there is almost no prior study on bending-excited early-barrier reactions, such as the F + methane reaction. Indeed the Polanyi rules 23 predict that the translational energy is more efficient to activate early-barrier reactions than vibrational excitation ͑and the reverse is true for the late-barrier reactions͒.…”

mentioning

confidence: 99%

Communication: Experimental and theoretical investigations of the effects of the reactant bending excitations in the F+CHD3 reaction

Czakó

Shuai

Liu

et al. 2010

The effects of the reactant bending excitations in the F+CHD3 reaction are investigated by crossed molecular beam experiments and quasiclassical trajectory (QCT) calculations using a high-quality ab initio potential energy surface. The collision energy (Ec) dependence of the cross sections of the F+CHD3(vb=0,1) reactions for the correlated product pairs HF(v′)+CD3(v2=0,1) and DF(v′)+CHD2(v4=0,1) is obtained. Both experiment and theory show that the bending excitation activates the reaction at low Ec and begins to inactivate at higher Ec. The experimental F+CHD3(vb=1) excitation functions display surprising peak features, especially for the HF(v′=3)+CD3(v2=0,1) channels, indicating reactive resonances (quantum effects), which cannot be captured by quasiclassical calculations. The reactant state-specific QCT calculations predict that the v5(e) bending mode excitation is the most efficient to drive the reaction and the v6(e) and v5(e) modes enhance the DF and HF channels, respectively.