一氧化二氮的光解动力学:O(^(1)D)+N_(2)(X^(1)∑_(g)^(+))产物通道

Photodissociation Dynamics of Nitrous Oxide:The O(^(1)D)+N_(2)(X^(1)∑_(g)^(+))Product Channel

由于一氧化二氮(N_(2)O)在大气化学中的重要性,本文使用时间切片的离子速度成像技术重新研究了一氧化二氮在紫外吸收区域的光解离动力学.采用单色光测量了203.814nm和205.472nm光解产物O(^(1)D)的离子影像,以及采用双色光记录了从200到220nm范围八个光解波长下解离产物O(^(1)D)的图像.产物N_(2)(X^(1)∑_(g)^(+))碎片的转动态分布和各向异性参数的信息可以从图像中获取:实验结果表明,N_(2)产物的转动态分布发生反转,最大值在J≈70.随着N_(2)转动量子数J增加,各向异性参数β表现出两次显著的下降.根据前人的理论计算[J,Chem.Phys.136,044314(2012)],初始线性构型的轴向反冲程度的不同导致了β随J的变化.然而,在高J区域,非绝热跃迁之后的基态势能面上存在额外的扭矩,从而引起额外的转动激发和较低的β值.采用真空紫外单光子电离O(^(1)D)原子的双色实验能够准确地获得产物的转动态分布和角分布.该工作加深了对三原子分子光解机制的进一步理解.

Photodissociation of nitrous oxide(N_(2)O)in the ultraviolet region has been revisited by using the time-sliced velocity map ion imaging technique,due to its importance in atmospheric chemistry.The images of O(^(1)D)photofragments are recorded at 203.814 nm and 205.472 nm in one-color experiments and at eight photolysis wavelengths between 200 and 220 nm in two-color experiments.The rotational state distributions and angular anisotropy parameters of the N_(2)(X^(1)∑_(g)^(+))co-products are derived from the images.The results indicate that the rotational state distributions are inverted with the maximum around J≈70.The anisotropy parameter β mainly shows two declines as the N_(2) rotational quantum number J increases.According to theoretical calculations[J.Chem.Phys.136,044314(2012)],the variations in β with J are caused by changes in the extent of axial recoil from a linear initial configuration.In the high-J region,however,additional torque exists on the ground state potential energy surface following nonadiabatic transitions,inducing both the additional rotational excitation and the lowerβvalues.Compared to previous works,the two-color experiments combined with single vacuum ultraviolet photonionization of O(^(1)D)allow us to acquire both the rotational state distribution and angular distribution accurately.This work deepens our understanding of triatomic molecule decomposition.