Gunthardt C E, Wallace C J, Hall G E, Field R W, North S W
Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
Chemistry Division , Brookhaven National Laboratory , Upton , New York 11973 , United States.
J Phys Chem A. 2019 Apr 4;123(13):2780-2788. doi: 10.1021/acs.jpca.9b00109. Epub 2019 Mar 13.
We report on one-color experiments near 214 nm involving the photodissociation of jet-cooled OCS to produce high rotational states (40 < J < 80) of CO (X Σ, v = 0, 1) which were then ionized by 2+1 resonance-enhanced multiphoton ionization via the E Π state. The nominally forbidden Q-branch of the two-photon E Π-X Σ transition is observed with intensity comparable to the allowed R-branch. The bright character of the high- J Q-branch lines can be described quantitatively as intensity borrowing due to mixing of the E Π and C Σ states, using J-dependent mixing coefficients extrapolated from the observed Λ-doubling in the lower rotational levels of the E state. In addition to the significant enhancement of Q-branch intensities above the values predicted by conventional two-photon line strengths for a Π-Σ transition, the high- J lines of the R- and P-branches appear to be suppressed in intensity by approximately a factor of 3 compared to the unperturbed low- J line strengths, most likely due to perturbations associated with a Σ state. The E-state rotational term values for J < 80, v = 0 derived from the present spectra agree within our measurement and calibration uncertainties with the extrapolations based on the molecular constants previously derived from rotational levels with J < 50. The E-X transition is attractive for future application to photodissociation dynamics and rotational polarization measurements of CO photofragments, with convenient access to state-selective probing on multiple rotational branches, which exhibit different sensitivity to fragment alignment.
我们报道了在214nm附近进行的单颜色实验，该实验涉及喷射冷却的OCS光解离以产生CO（X Σ，v = 0, 1）的高转动能级（40 < J < 80），然后通过E Π态经由2 + 1共振增强多光子电离使其电离。观察到双光子E Π - X Σ跃迁中名义上禁戒的Q支，其强度与允许的R支相当。高J值Q支谱线的明亮特征可以定量地描述为由于E Π和C Σ态混合导致的强度借用，使用从E态较低转动能级中观察到的Λ双重分裂外推得到的与J相关的混合系数。除了Q支强度显著高于由常规双光子线强预测的Π - Σ跃迁的值外，R支和P支的高J值谱线强度相比于未受扰动的低J值线强似乎被抑制了约3倍，这很可能是由于与一个Σ态相关的扰动。从当前光谱推导得到的J < 80、v = 0时E态的转动项值，在我们的测量和校准不确定度范围内，与基于先前从J < 50的转动能级推导得到的分子常数所做的外推结果一致。E - X跃迁对于未来应用于CO光解离动力学和CO光碎片的转动极化测量具有吸引力，因为可以方便地对多个转动支进行态选择探测，这些转动支对碎片取向表现出不同的灵敏度。
