Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
J Chem Phys. 2011 Jul 14;135(2):024311. doi: 10.1063/1.3602324.
The energy partitioning in the UV photodissociation of N(2)O is investigated by means of quantum mechanical wave packet and classical trajectory calculations using recently calculated potential energy surfaces. Vibrational excitation of N(2) is weak at the onset of the absorption spectrum, but becomes stronger with increasing photon energy. Since the NNO equilibrium angles in the ground and the excited state differ by about 70°, the molecule experiences an extraordinarily large torque during fragmentation producing N(2) in very high rotational states. The vibrational and rotational distributions obtained from the quantum mechanical and the classical calculations agree remarkably well. The shape of the rotational distributions is semi-quantitatively explained by a two-dimensional version of the reflection principle. The calculated rotational distribution for excitation with λ = 204 nm and the translational energy distribution for 193 nm agree well with experimental results, except for the tails of the experimental distributions corresponding to excitation of the highest rotational states. Inclusion of nonadiabatic transitions from the excited to the ground electronic state at relatively large N(2)-O separations, studied by trajectory surface hopping, improves the agreement at high j.
利用最新计算的势能面，通过量子力学波包和经典轨迹计算研究了 N(2)O 在紫外光解中的能量分配。在吸收光谱的起始处，N(2)的振动激发很弱，但随着光子能量的增加而增强。由于基态和激发态的 NNO 平衡角相差约 70°，因此分子在碎片化过程中经历了非常大的扭矩，产生了非常高的转动态的 N(2)。从量子力学和经典计算中得到的振动和转动分布非常吻合。通过二维反射原理的一个版本，对转动分布的形状进行了半定量解释。对于 λ = 204nm 的激发，计算得到的转动分布与 193nm 的平移能分布与实验结果非常吻合，除了与激发最高转动态相对应的实验分布的尾部。通过轨迹表面跳跃研究了在相对较大的 N(2)-O 分离处从激发态到基态电子态的非绝热跃迁的包含，提高了在高 j 时的吻合度。
