利用CARS技术研究激发态Rb_2和H_2的碰撞转移

Study of the Energy Transfer between Excited Rb_2 and H_2 Using the CARS Technique

利用相干反斯托克斯拉曼光谱(coherent anti-stokes Raman spectroscopy,CARS)探测技术,研究了激发态Rb2与H2间的电子-振转能级的碰撞转移。扫描CARS谱确认了H2分子仅在ν=1,J=1,2及ν=2,J=0,1,2能级上有布居,用n1,n2,n3,n4,n5分别表示(2,0),(2,1),(2,2),(1,1)及(1,2)上的粒子数密度。从CARS线的峰值得到n1/n5,n2/n5,n3/n5,n4/n5分别为3.57±0.71,2.65±0.53,3.00±0.60和0.93±0.17,有83%粒子数处在ν=2的振动能级上,而在ν=1上为17%,转移能配置到振动,转动,平动的比例分别为0.48,0.01,和0.51,能量主要分配在振动和平动上。在T=573K和PH2=5×103 Pa条件下,通过求解速率方程组和对时间分辨CARS线轮廓的分析,得到碰撞转移速率系数k12=(3.1±0.6)×10-14 cm-3.s-1和k2=(4.9±1.0)×10-15 cm-3.s-1。

Using the CARS（coherent anti-Stokes Raman spectroscopy） detection technique,the authors investigated the electronic-to-rovibrational levels energy transfer between electronically excited Rb2 and H2.In this CARS experiment,the S-branch（Δν=1,ΔJ=2） transition of H2 was excited by two laser pulses,the pump and the Stokes,respectively,centered at 532 and 690 nm.The internal state distribution of collisionally populated H2 was probed.The scanned CARS spectra reveal that during energy transfer processes H2 molecules were produced only at the ν=1,J=1,2 and ν=2,J=0,1,2 rovibrational levels.From scanned CARS spectral peaks the population ratios were obtained.The n1/n5,n2/n5,n3/n5 and n4/n5 are 3.57±0.71,2.65±0.53,3.00±0.60 and 0.93±0.17,respectively,where n1,n2,n3,n4 and n5 represent the number densities of H2 at the rovibrational levels（2,0）,（2,1）,（2,2）,（1,1） and（1,2）, respectively.The population ratios indicate that the H2 molecules produced by the energy transfer process are 83% populated at the ν=2 vibrational level and 17% at ν=1.The relative fractions（〈fV〉∶〈fR〉∶〈fT〉= of average energy disposal were derived as（0.48,0.01,0.51）,with major translational and vibrational energy release.Through semilog plot of the time-resolved CARS profiles under a simple kinetic model under the experimental conditions of T=573 K and P=5×103 Pa,the collisional transfer rate coefficients k12=（3.1±0.6）×10-14 cm-3·s-1 and k2=（4.9±1.0）×10-15 cm-3·s-1 have been obtained.