Arrowsmith Alan N, Chikan Viktor, Leone Stephen R
Department of Chemistry and Biochemistry, JILA, National Institute of Standards and Technology, University of Colorado, Boulder, Colorado 80309, USA.
J Phys Chem A. 2006 Jun 22;110(24):7521-6. doi: 10.1021/jp061246e.
The reaction C(2)H + O(2) --> CH(A(2)Delta) + CO(2) is investigated using Fourier transform visible emission spectroscopy. C(2)H radicals, produced by 193 nm photolysis of C(2)H(2), react with O(2) molecules at low total pressures to produce electronically excited CH(A(2)Delta). Observation of the CH(A(2)Delta-X(2)Pi) electronic emission to infer nascent rotational and vibrational CH(A(2)Delta) distributions provides information about energy partitioning in the CH(A(2)Delta) fragment during the reaction. The rotational and vibrational populations of the CH(A(2)Delta) product are determined by fitting the rotationally resolved experimental spectra with simulated spectra. The CH(A(2)Delta) product is found to be rotationally and vibrationally excited with T(rot) congruent with 1150 K and T(vib) congruent with 1900 K. The mechanism for this reaction proceeds through one of two five-atom intermediates and requires a crossing between electronic potential surfaces. The rotational excitation suggests a bent geometry for the final intermediate of this reaction before dissociation to products, and the vibrational excitation involves an elongation of the C-H bond from the compressed transition state to the final CH(A) state.
利用傅里叶变换可见发射光谱对反应C(2)H + O(2) --> CH(A(2)Δ) + CO(2)进行了研究。由193nm光解C(2)H(2)产生的C(2)H自由基在低总压下与O(2)分子反应生成电子激发态的CH(A(2)Δ)。通过观察CH(A(2)Δ-X(2)Π)电子发射来推断新生的转动和振动CH(A(2)Δ)分布，可提供有关反应过程中CH(A(2)Δ)碎片能量分配的信息。通过将旋转分辨的实验光谱与模拟光谱拟合来确定CH(A(2)Δ)产物的转动和振动布居。发现CH(A(2)Δ)产物的转动和振动被激发，其转动温度T(rot)约为1150K，振动温度T(vib)约为1900K。该反应的机理通过两种五原子中间体之一进行，并且需要在电子势能面之间交叉。转动激发表明该反应最终中间体在解离为产物之前具有弯曲的几何形状，而振动激发涉及C-H键从压缩的过渡态到最终CH(A)态的伸长。
