振动激发KH与CO2碰撞中能量的时间分辨分布

摘要

ThevibrationallevelsofKH(Х1Σ+ ν″=0~3)weregeneratedinthereactionofK(5P)withH2 .Thevibrationallyex-cited KH(ν″=17) was populated by an overtone pump-probe configuration .Different characteristics of collisional energy transfer in highly and lowly excited vibrational levels of KH and CO2 were investigated through measuring the time-resolved distribution of vibrational energy in KH(ν″=17 ,3)+CO2 collisions .For KH(ν″=17) ,there existed three principal regions of vibration tem-perature (Tν) in this equilibration process .The initial phase consists of very rapid fall in Tνwithin ~5 μs ,and the vibrational energy of KH(ν″=17) is mainly transferred to the vibrational levels of CO2 (0001) or high rotational levels of CO2 (0000) .The second phase (5~20 μs) has a slight decline in Tν,and the process of energy transfer to vibrational levels or high rotational lev-els of CO2 has already finished .The vibration temperature of the third phase has a slightly more rapid decline compared with the last phase .This phase shows that the process of transfer to lowly rotational levels and translation energy of CO 2 is accelerated . The equilibration of vibrationally excited KH (ν″=3) in CO2 was also investigated .There are similarities to the behavior of KH (ν″=17) in CO2 plot ,but also are significant differences .Once the initial resonant V-R exchange has equalized vibrational tem-peratures ,there is a very slow linear decline in Tνwith equilibrium attained within ~80 μs .This same point is reached within 15μs for KH (ν″=17) .The data demonstrate that single rate coefficient measurements are unlikely to capture the complex nature of processes that generally are multistaged with different relaxation rates characterizing each different stage .Examination of the quantum state distributions reveals that these distinct stages reflect the dominance of specific energy transfer mechanisms ,some of which are inherently fast and others are much slower .The energy gain into CO2 resulting from collisions with excited KH was probed using transient absorption techniques .Distributions of nascent CO2 rotational populations in both ground (0000) state and the vibrationally excited (0001) state were determined .A kinetic model was developed to describe rate coefficients for ap-pearance of CO2 states resulting from collisions with excited KH .These experiments show that collisions resulting in CO2 (0000) are accompanied by substantial excitation in rotation while the vibrationally excited CO 2 (0001) state has rotational energy distri-butions near the initial distributions .%K（5P）与 H2反应产生KH（Х1Σ＋）的ν″＝0～3振动能级，泛频激发KH至ν″＝17高位振动态。通过测定KH（ν″＝17，3）与CO2碰撞过程中振动能的时间分辨分布（即 Tν的变化过程），研究了高低振动态碰撞传能的不同特点。对于KH（ν″＝17），振动温度 Tν的变化分为三个阶段：第一阶段（0～5μs）Tν迅速下降，能量应主要转移至CO2（0001）振动态或（0000）高位转动态；第二阶段（5～20μs）Tν仅稍有下降，向CO2振动态及高位转动态的能量转移已结束；第三阶段（20μs后） Tν虽然缓慢但明显下降，表明向CO2低转动态及平动能的转移加速。对于KH（ν″＝3），Tν的变化只分为两个阶段：第一阶段（0～10μs）的共振V-R过程迅速降低了振动温度；第二阶段（10～80μs ） Tν有一个缓慢下倾，只能转移到很低的转动态和小的平动能。这些结果表明了振动激发态分子与基态分子碰撞中仅用单一速率系数不能正确揭示复杂平衡过程的本质，不同的阶段应该用不同的速率系数来描述。利用瞬时吸收技术得到CO2（0000）和（0001）的原生态转动布居分布，通过速率方程分析，得到平衡过程中不同阶段的速率系数。