CsH(X^1Σ^+,v≥15)与CO_2碰撞中的振动-转动能量转移

Vibrational to Rotational Energy Transfer between CsH(X^1Σ^+,v≥15) and CO_2

研究了高位振动激发态CsH(v″=15～21)与CO2振动-转动碰撞转移过程。脉冲激光激发CsH至高振动态,利用激光感生荧光光谱(LIF)得到CsH(v″)与CO2的猝灭速率系数kv″(CO2),kv″=21(CO2)=7kv″=15(CO2)。研究了CsH(v″)+H2的弛豫过程,有kv″(H2)>kv″(CO2),碰撞弛豫速率系数的质量效应明显。利用激光泛频光谱技术,测量了CO2(0000)的转动态分布。对于CO2与CsH(v″=15)碰撞,CO2有转动温度Trot=(605±50)K;对于v″=21,Trot=(780±70)K。基于转动温度,得到CO2的平均转动能〈Erot〉和转动能的变化〈ΔErot〉,发现〈ΔErot〉v″=21～2.7〈ΔErot〉v″=15。由对CO2转动能级受激吸收线轮廓测量,得到J=36～48各能级的平均平动能〈Erel〉,对于v″=15,〈Erel〉=600～972cm-1;对于v″=21,〈Erel〉=972～1 351cm-1。低J值有低平动能。外推平动能到初始平动能520cm-1(池温500K的平动能)对于v″=15和v″=21,分别得到阈值Jth=34和24。大于初始平动能的转动态均处于Jth值之上。

The quenching of highly vibrational excited CsH through collisions with a 500 K bath of CO2 was investigated using the laser spectroscopy technique.CsH was formed by the Cs（7P）＋H2 reaction.The pulse laser prepared CsH in the highly vibrational levels.Laser induced fluorescence was used to detect collisionally relaxed CsH.The relaxation rate coefficient of CsH（v″=21） with CO2 is 10 times larger than that of CsH（v″=15）.Relaxation of CsH（v″） with H2 was also investigated.The mass effect on the collisional relaxation rate coefficients is strong.The observed collisional relaxation rate coefficients of H2 are bigger than those of CO2.Energy gain into CO2 resulting from collisions with excited CsH was probed using laser overtone spectroscopy technique.Distributions of nascent CO2 rotational population in the ground（0000） state were determined.For CsH excited at v″=15,the scattered CO2 molecules have a rotational temperature of Trot=（605±50） K.For excitation at v″=21,the CO2 rotational temperature is Trot=（780±70） K.Based on the rotational temperatures,the average change in the CO2 rotational energy 〈ΔErot〉 has a stronger dependence on the CsH initial energy.Using the ambient cell temperature,〈ΔErot〉v″=21~2.7〈ΔErot〉v″=15 was found.The nascent distributions of recoil velocities for collisions were determined from stimulated absorption line profiles of individual CO2 rotational states.For v″=15,scattered CO2 molecules with J=36-48 have center of mass translational energy of 〈Erel〉=600~972 cm-1.For v″=21,the values increase to 〈Erel〉=972~1 351 cm-1.Based on propensity rules for collisions that favor small changes in energy and angular momentum,it is reasonable that low-J CO2 states will have lower translational energy than the high-J states.Extrapolating v″=15 and 21 data to the initial relative translational energy of E0=520 cm-1 gives an estimate of the threshold states Jth=34 and 24,respectively.The onset of large 〈Erel〉 is likely to occur at J states that are larger than Jth.