Ogden Hannah M, Michael Tara J, Murray Matthew J, Liu Qingnan, Toro Carlos, Mullin Amy S
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
Phys Chem Chem Phys. 2019 Jul 3;21(26):14103-14110. doi: 10.1039/c8cp06917d.
The effect of CO rotational energy on bimolecular reactions to form electronically excited C2 is reported here. The reactions are initiated by CO multiphoton absorption of 800 nm light in strong optical fields using two different polarization configurations based on shaped chirped pulses. The observation of Swan band emission indicates that C2(d3Πg) is a reaction product. The optical polarization is in the form of either an optical centrifuge or a dynamic polarization grating. In each case, the strong field aligns CO molecules and induces multiphoton absorption. Power-dependent measurements indicate at least seven photons are absorbed by CO; CO(a3Π) is a likely reactant candidate based on kinetic modeling. Relative reaction efficiencies are determined by measuring Swan band emission intensities. For a CO pressure of 100 Torr and an optical intensity of I = 2.0 × 1013 W cm-2, the relative C2(d3Πg) yield with the dynamic polarization grating is twice that with the optical centrifuge. The extent of CO rotational energy was determined for both optical polarizations using high-resolution transient IR absorption for a number of CO states with J = 62-73 and Erot up to 10 400 cm-1. Optical centrifuge excitation generates at least 2.5 times more rotationally excited CO molecules per quantum state than the dynamic polarization grating. The results indicate that the effect of large amounts of CO rotational energy is to reduce the yield of the C2 products.
本文报道了CO转动能对形成电子激发态C2的双分子反应的影响。反应通过在强光学场中利用基于啁啾脉冲整形的两种不同偏振配置对800 nm光进行CO多光子吸收来引发。对天鹅带发射的观测表明C2(d3Πg)是反应产物。光偏振采用光学离心机或动态偏振光栅的形式。在每种情况下，强场使CO分子取向并诱导多光子吸收。功率相关测量表明CO至少吸收七个光子；基于动力学模型，CO(a3Π)是可能的反应物候选物。通过测量天鹅带发射强度来确定相对反应效率。对于100 Torr的CO压力和I = 2.0×1013 W cm-2的光强度，动态偏振光栅的相对C2(d3Πg)产率是光学离心机的两倍。利用高分辨率瞬态红外吸收，针对J = 62 - 73且Erot高达10 400 cm-1的多个CO态，确定了两种光偏振下CO转动能的程度。每个量子态中，光学离心机激发产生的转动激发CO分子比动态偏振光栅至少多2.5倍。结果表明，大量CO转动能的作用是降低C2产物的产率。
