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Rotational Distributions and Imaging of Singlet O2 Following Spin-Forbidden Photodissociation of O3
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2023-08-04 , DOI: 10.1021/acs.jpca.3c02736
Megan N Aardema 1 , Megan Fast 1 , Benjamen Meas 1 , Simon W North 1
Affiliation  

We report REMPI spectra and velocity-mapped ion images of the O2(a1Δg) and (b1Σg+) fragments arising from the spin-forbidden photodissociation of O3 near 320 and 330 nm. The O2(a1Δg, v = 0) REMPI spectrum following a 320 nm dissociation shows enhanced peak intensity for the odd rotational states relative to the even states, which is the opposite of the trend observed by Gunthardt et al. ( J. Chem. Phys. 2019, 151, 224302) for spin-allowed dissociation at 266 nm but is consistent with the couplings between the B state and 3A′ and 3A″ states calculated by Grebenshchikov and Rosenwaks ( J. Phys. Chem. A 2010, 114, 9809–9819). There are no significant differences between the ion image angular distributions of fragments in odd and even rotational states, which indicates a cold distribution of O3 and supports the explanation that the alternation in peak intensities results from a difference in the couplings. Quantitative analysis of the image angular distributions was limited due to the single laser polarization geometry accessible in one-color experiments. Radial distributions of the 320 nm images indicate a broad rotational distribution, evidenced in bimodal speed distributions with peaks corresponding to both high (j = 35–43) and low (j = 17–20) rotational states. The REMPI spectrum of O2(a1Δg) near 330 nm was collected, and while quantitative population analysis is difficult because of the perturbed resonant state, the spectrum clearly supports a broad rotational distribution as well, consistent with the images collected at 320 nm. A 2D-REMPI spectrum was collected following dissociation of O3 near 330 nm, which showed evidence of contributions from O2 fragments in both the a1Δg and b1Σg+ states. The rotational distribution for the O2(b1Σg+, v = 0) product peaks at j = 32 and is narrower than that of the O2(a1Δg) fragment, consistent with distributions reported by O’Keeffe et al. at longer dissociation wavelengths ( J. Chem. Phys. 2002, 117, 8705–8709). At smaller radii in the 2D-REMPI spectrum, there is additional signal assigned to v = 1–4 of O2(b1Σg+), with rotational distributions similar to v = 0. The vibrational distribution of the O2(b1Σg+) fragment peaks at v = 0, with populations monotonically decreasing with increasing vibrational state. Ion image angular distributions of the O2(b1Σg+) fragment and the corresponding anisotropy parameters are also reported.

中文翻译:


O3 自旋禁止光解离后单线态 O2 的旋转分布和成像



我们报告了 O 3在 320 和 330 nm 附近的自旋禁止光解离产生的 O 2 ( a 1 Δ g ) 和 ( b 1 Σ g + ) 碎片的 REMPI 谱和速度映射离子图像。 320 nm 解离后的 O 2 ( a 1 Δ g , v = 0) REMPI 光谱显示奇数旋转态相对于偶数态的峰值强度增强,这与 Gunthardt 等人观察到的趋势相反。 ( J. Chem. Phys. 2019 , 151 , 224302 ) 对于 266 nm 处的自旋允许解离,但与 Grebenshchikov 和 Rosenwaks 计算的 B 态与3 A′ 和3 A” 态之间的耦合一致 ( J. Phys. 2019 , 151 , 224302 )。化学 2010,114,9809-9819 )。奇数和偶数旋转状态下碎片的离子图像角分布没有显着差异,这表明O 3的冷分布,并支持峰强度交替是由耦合差异引起的解释。由于单色实验中可访问的单一激光偏振几何结构,图像角度分布的定量分析受到限制。 320 nm 图像的径向分布表明了广泛的旋转分布,这在双峰速度分布中得到了证明,其峰值对应于高 ( j = 35–43) 和低 ( j = 17–20) 旋转状态。 收集了 330 nm 附近的 O 2 ( a 1 Δ g ) 的 REMPI 光谱,虽然由于共振态受到扰动,定量总体分析很困难,但该光谱也清楚地支持广泛的旋转分布,与 320 nm 处收集的图像一致纳米。 O 3在 330 nm 附近解离后收集了 2D-REMPI 光谱,这表明 O 2碎片在a 1 Δ gb 1 Σ g +状态下都有贡献。 O 2 ( b 1 Σ g + , v = 0) 产物的旋转分布在j = 32 处达到峰值,并且比 O 2 ( a 1 Δ g ) 片段的旋转分布更窄,与 O'Keeffe 等人报道的分布一致等人。在较长的解离波长下( J. Chem. Phys. 2002 , 117 , 8705–8709)。在 2D-REMPI 谱中较小的半径处,有附加信号分配给 O 2 ( b 1 Σ g + ) 的 v = 1–4,其旋转分布类似于 v = 0。O 2 ( b的振动分布1 Σ g + ) 碎片在 v = 0 处达到峰值,数量随着振动状态的增加而单调减少。 还报告了 O 2 ( b 1 Σ g + ) 碎片的离子图像角分布和相应的各向异性参数。
更新日期:2023-08-04
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