Department of Chemistry, Grand Valley State University, Allendale, Michigan 49401, USA.
J Chem Phys. 2012 Jan 28;136(4):044314. doi: 10.1063/1.3679171.
The angular distribution of products from the ultraviolet photodissociation of nitrous oxide yielding O((1)D) and N(2)(X Σ(g)(+)(1)) was investigated using classical trajectory calculations. The calculations modeled absorption only to the 2(1)A(') electronic state but used surface-hopping techniques to model nonadiabatic transitions to the ground electronic state late in the dissociation. Observed values of the anisotropy parameter β, which decrease as the product N(2) rotational quantum number j increases, could be well reproduced. The relatively low observed β values arise principally from nonaxial recoil due to the very strong bending forces present in the excited state. In the main part of the product rotational distribution near 203 nm, an unusual dynamical effect produces the decrease in β with increasing j; nonaxial recoil effects remain approximately constant while higher j product molecules arise from parent molecules that had their transition dipole moments aligned more closely along the molecular axis. In both low and high j tails of the rotational distribution, the variations in β with j are caused by changes in the extent of nonaxial recoil. In the high-j tail, additional torque present on the ground state potential energy surface following nonadiabatic transitions causes both the additional rotational excitation and the lower β values.
使用经典轨迹计算研究了一氧化二氮的紫外光解产物的角分布，生成 O((1)D) 和 N(2)(X Σ(g)(+)(1))。计算仅模拟了到 2(1)A(') 电子态的吸收，但使用表面跳跃技术在离解后期模拟了非绝热跃迁到基态电子态。观察到的各向异性参数 β 值随产物 N(2)转动量子数 j 的增加而减小，可以很好地重现。观察到的相对较低的 β 值主要来自于激发态中存在的非常强的弯曲力引起的非轴向反冲。在 203nm 附近的主要产物转动分布部分，一种不寻常的动力学效应导致 β 值随 j 的增加而减小；非轴向反冲效应基本保持不变，而更高 j 的产物分子则来自于其跃迁偶极子更接近分子轴的母体分子。在转动分布的低 j 和高 j 尾部，β 值随 j 的变化是由非轴向反冲程度的变化引起的。在高 j 尾部，非绝热跃迁后在基态势能面上存在的额外扭矩导致了额外的转动激发和较低的 β 值。
