Direct Ab Initio Dynamics Study of Radical C<sub>4</sub>H (X̃<sup>2</sup>Σ<sup>+</sup>) + CH<sub>4</sub> Reaction HuoRui-Ping ZhangXiang HuangXu-Ri LiJi-Lai SunChia-Chung 2011 The methane (CH<sub>4</sub>) hydrogen abstraction reaction by linear butadiynyl radical C<sub>4</sub>H (CCCCH) has been investigated by direct ab initio dynamics over a wide temperature range of 100−3000 K, theoretically. The potential energy surfaces (PESs) have been constructed at the CCSD(T)/aug-cc-pVTZ//BB1K/6-311G(d,p) levels of theory. Two different hydrogen abstraction channels by C<sup>1</sup> and C<sup>4</sup> of C<sub>4</sub>H (C<sup>1</sup>C<sup>2</sup>C<sup>3</sup>C<sup>4</sup>H) have been considered. The results indicate that the C<sup>1</sup> position of C<sub>4</sub>H is a more reactive site. The electron transfer behaviors of two possible channels are also analyzed by quasi-restricted orbital (QRO) in detail. The rate constants calculated by canonical variational transition-state theory (CVT) with the small-curvature tunneling correction (SCT) are in excellent agreement with available experimental values. The normal and three-parameter expressions of Arrhenius rate constants are also provided within 100−3000 K. It is expected to be helpful for further studies on the reaction dynamics behaviors over a wide temperature range where no experimental data is available so far.