Parsons Bradley F, Pappas Emerson, Reardon Kylie, Loder Kathleen
Department of Chemistry and Biochemistry, Creighton University, 2500 California Plaza, Omaha, Nebraska 68178, United States.
ACS Omega. 2025 Sep 8;10(37):43179-43186. doi: 10.1021/acsomega.5c06670. eCollection 2025 Sep 23.
We have photodissociated the Ar-NO complex from 4 to 337 cm above the energy required to form NO (A ∑). In the experiment, the NO (A) product was nonresonantly ionized, and velocity map ion images were recorded at a resolution sufficient to identify individual rotational states. From the data, we determined the minimum energy required to form the NO (A) product to be 44294.3 ± 2.2 cm. We also determined the ground state dissociation energy for Ar-NO to be 95.4 ± 2.2 cm and the excited-state dissociation energy to be 52 ± 2 cm. The ground-state dissociation energy agrees with experimental results and a recent three-dimensional potential energy surface; however, the excited-state dissociation energy is larger than predicted by theoretical surfaces. We also determined the NO (A) rotational state distribution, which was bimodal due to the rotational rainbow effect and showed significantly less contribution from hotbands compared with previous experiments. Our data also allowed for measurement of the angular anisotropy parameter, β, over the range of NO (A) rotational states. We observed that for the lowest rotational levels, β changes from ∼ -0.3 at low excitation energy to ∼+0.4 at high excitation energy, which is consistent with previous work. Furthermore, we report β values for the highest rotational states formed at each excitation energy. Our experiment demonstrated that for a given excitation energy, the high rotational states consistently exhibited a more negative β compared with the low rotational levels. Qualitatively, this behavior can be attributed to excitation to regions of the excited state resembling a skewed T-shape that then dissociate to high NO (A) rotational levels with β ≤ 0.
我们已将Ar-NO复合物光解离至比形成NO（A ∑）所需能量高4至337厘米的范围。在实验中，NO（A）产物被非共振电离，并以足以识别各个转动状态的分辨率记录速度映射离子图像。根据数据，我们确定形成NO（A）产物所需的最小能量为44294.3±2.2厘米。我们还确定Ar-NO的基态解离能为95.4±2.2厘米，激发态解离能为52±2厘米。基态解离能与实验结果和最近的三维势能面一致；然而，激发态解离能大于理论表面的预测值。我们还确定了NO（A）转动状态分布，由于转动彩虹效应，该分布是双峰的，并且与先前的实验相比，热带的贡献明显减少。我们的数据还允许在NO（A）转动状态范围内测量角各向异性参数β。我们观察到，对于最低转动能级，β在低激发能量下从约-0.3变化到高激发能量下的约+0.4，这与先前的工作一致。此外，我们报告了在每个激发能量下形成的最高转动状态的β值。我们的实验表明，对于给定的激发能量，与低转动能级相比，高转动状态始终表现出更负的β。定性地说，这种行为可归因于激发到类似于倾斜T形的激发态区域，然后解离为β≤0的高NO（A）转动能级。
