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Dynamics Study on the Multi-Photon Dissociation of CS2+ to CS+
Wang Feng, Zhang Limin, Wang Zhong, Hou Yi, Ren Wenqing, Zhuang Xiujuan, Yu Shuqin*
Laboratory of Bond Selective Chemistry,Department of Chemical Physics,University of Science and Technology of China,Hefei 230026
Abstract:
The dynamics on the multi-photon dissociation of CS2+ molecular ions to produce CS + ions has been investigated by measuring the CS + photofragment excitation(PHOFEX)spectrum in the wavelength range of 385~435 nm,where the CS2+ molecular ions were prepared purely by[3+1]multiphoton ionization of the neutral CS2molecules at 483.2 nm. With the ~60 ns delay,which is much more than the laser pulse width(~5 ns),between ionization laser and dissociation laser,the threshold wavelength of dissociation laser to produce CS+ fragment ion from CS2+ molecular ions was obviously observed in the PHOFEX spectrum. The adiabatic appearance potential of the CS+ was determined to be(5.852 ± 0.005)eV above the X 2Σg,3/2(0,0,0)level of CS2+. The product branching ratios,(CS+/S+),as measured from the PHOFEX spectra,increase from 0 to slightly larger than 1 in the wavenumber range of 47200~50400 cm-1 . The[1+1]dissociation mechanism to get to CS++S from CS2+ was discussed and preliminarily attributed to(i)CS2+(X 2Πg)→ CS2+(A2Πu)through one-photon excitation,(ii)CS2+(A2Πu)→ CS2+(X*)via internal conversion process due to the vibronic coupling between the A and X states,(iii)CS2+(X*)→ CS2+(B 2Σ+u)through the second photon excitation,and(iv)CS2+(B 2Σ+u)→CS +(X 2Σ+)+S(3P),because of the potential curve crossing with the repulsive 4Σ- state and/or the 2Σ- state correlated with the second dissociation limit. However,when the dissociation laser overlaps the ionization laser in time scale in the laser-molecule interaction zone,the appearance threshold is not available in the PHOFEX spectrum. This fact shows that there are other mixed three-photon paths of[1+1+1'],[1+1'+1'],and[1+1'+1]to produce CS+ fragment ion from CS2+ molecular ions besides the above[1+1]dissociation mechanism,that is,CS2+(X 2Πg)→ CS2+(A 2Πu)through one-photon excitation[1]of dissociation laser,CS2+(A 2Πu)→CS2+(X*)via internal conversion process due to the vibronic coupling between the A and X states,CS2+(X*)→ CS2+(B 2Σ +u)through the second photon excitation by dissociation laser[1]or ionization laser[1'],and third photon excitation by ionization laser[1']or dissociation laser[1]to reach the adiabatic appearance potential to produce CS+ with the dissociation laser wavelengths longer than 423. 89 nm,at which the[1+1]dissociation mechanism to get to CS+ is unavailable.
Key words:  CS2+,Photodissociation,Photofragment excitation
FundProject:
CS2+多光子光解产生CS+的动力学研究
王峰, 张立敏, 王仲, 侯毅, 任文清, 庄秀娟, 俞书勤*
中国科学院选键化学开放实验室,中国科学技术大学化学物理系,合肥 230026
摘要:
在射流气束条件下,利用第一束483.2 nm的电离激光使中性CS2分子通过(3+1)共振增强多光子电离(REMPI)制备出纯净的CS2+分子离子;用第二束解离激光在385~435 nm扫描,由获得的光解离碎片激发(PHOFEX)谱研究了光解CS2+产生CS+的两种动力学途径. 当第一束电离激光和第二束解离激光在时间上有约60 ns 的延迟(远大于激光脉宽约5 ns)时,光解CS2+母体离子产生CS+碎片离子有明显的阈值效应,由PHOFEX谱确定了CS+的绝热出现势(5.852±0.005)eV(从CS2+
关键词:  CS2+  光解离  光碎片激发
DOI:10.1088/1674-0068/17/3/309-316
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