Chao Wen, Jones Gregory H, Okumura Mitchio, Percival Carl J, Winiberg Frank A F
Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, California 91125, United States.
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109-8099, United States.
J Phys Chem A. 2023 Oct 12;127(40):8374-8382. doi: 10.1021/acs.jpca.3c04977. Epub 2023 Sep 29.
Sulfur oxide species (RSO) play a critical role in many fields, ranging from biology to atmospheric chemistry. Chlorine-containing sulfur oxides may play a key role in sulfate aerosol formation in Venus' cloud layer by catalyzing the oxidation of SO to SO via sulfinyl radicals (RSO). We present results from the gas-phase UV-vis transient absorption spectroscopy study of the simplest sulfinyl radical, ClSO, generated from the pulsed-laser photolysis of thionyl chloride at 248 nm (at 40 Torr of N and 292 K). A weak absorption spectrum from 350 to 480 nm with a peak at 385 nm was observed, with partially resolved vibronic bands (spacing = 226 cm), and a peak cross section σ(385 nm) = (7.6 ± 1.9) × 10 cm. From calculations at the EOMEE-CCSD/ano-pVQZ level, we assigned this band to 1A' ← XA″ and 2A' ← XA″ transitions. The spectrum was modeled as a sum of a bound-to-free transition to the 1A' state and a bound-to-bound transition to the 2A' state with similar oscillator strengths; the prediction agreed well with the observed spectrum. We attributed the vibronic structure to a progression in the bending vibration of the 2A' state. Further calculations at the XDW-CASPT2 level predicted a conical intersection between the excited 1A' and 2A' potential energy surfaces near the Franck-Condon region. The geometry of the minimum-energy conical intersection was similar to that of the ground-state geometry. The lack of structure at shorter wavelengths could be evidence of a short excited-state lifetime arising from strong vibronic coupling. From simplified molecular orbital analysis, we attributed the ClSO spectrum to transitions involving the out-of-plane π/π orbitals along the S-O bond and the in-plane orbital possessing a σ/σ character along the S-Cl bond. We hypothesize that these orbitals are common to other sulfinyl radicals, RSO, which would share a combination of a strong and a weak transition in the UV (near 300 nm) and visible (400-600 nm) regions.
硫氧化物（RSO）在从生物学到大气化学等许多领域都起着关键作用。含氯硫氧化物可能通过亚磺酰基自由基（RSO）催化SO氧化为SO，从而在金星云层中硫酸盐气溶胶的形成中发挥关键作用。我们展示了对最简单的亚磺酰基自由基ClSO进行气相紫外可见瞬态吸收光谱研究的结果，该自由基是通过在248 nm（在40 Torr的N和292 K下）对亚硫酰氯进行脉冲激光光解产生的。观察到在350至480 nm范围内有一个弱吸收光谱，峰值在385 nm，有部分分辨的振动带（间距 = 226 cm），峰值截面σ(385 nm) = (7.6 ± 1.9) × 10 cm。通过在EOMEE - CCSD/ano - pVQZ水平的计算，我们将此带归属为1A' ← XA″和2A' ← XA″跃迁。该光谱被模拟为到1A'态的束缚到自由跃迁和到2A'态的束缚到束缚跃迁的总和，具有相似的振子强度；预测结果与观察到的光谱吻合良好。我们将振动结构归因于2A'态弯曲振动的进展。在XDW - CASPT2水平的进一步计算预测在弗兰克 - 康登区域附近激发的1A'和2A'势能面之间存在一个锥形交叉点。最低能量锥形交叉点的几何形状与基态几何形状相似。较短波长处缺乏结构可能是由于强振动耦合导致激发态寿命较短的证据。通过简化分子轨道分析，我们将ClSO光谱归因于涉及沿S - O键的面外π/π轨道和沿S - Cl键具有σ/σ特征的面内轨道的跃迁。我们假设这些轨道对于其他亚磺酰基自由基RSO是常见的，它们在紫外（近300 nm）和可见光（400 - 600 nm）区域将共享强跃迁和弱跃迁的组合。
