UV laser photodissociation of molecular ions

Abstract

An apparatus is described for performing molecular ion photofragment spectroscopy with an ultraviolet laser. Preliminary results are given for the photodissociation of H+2 , HD+, D+2 , D2O+, OD+, ND+3 , and ND+2 , using a laser energy of 6.42 eV. Where energetics permit alternative modes of dissociation, selectivity is observed and attributed to selection rules and correlation rules. With polyatomic ions, the distribution of recoil energies provides insight into the partition of excess energy between internal and kinetic energies of products. In the decomposition of ND+3 , results are obtained which call into question some recently reported thermochemical quantities.

Classical Dynamics Study of the Unimolecular Decomposition of CH3SH+

“…Fenn et al 1 attributed the high yield of CH 3 + + SH "to the more efficient translational to vibrational energy transfer for the C-S stretch than for the C-H stretches of CH 3 SH + , and to weak couplings between the low-frequency C-S and the high-frequency C-H stretching vibrational modes of CH 3 SH + ". In contrast, the breakdown diagrams of CH 3 SH + obtained in the charge-exchange, 10 PEPICO, 11 and photoionization mass spectrometric 9 experiments agree qualitatively with that predicted by Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. 9 Motivated by such evidence for nonstatistical behavior, we performed classical trajectory and RRKM calculations for three decomposition channels of the mercapto cation:…”

“…The mercapto cation (CH 3 SH + ) has been the focus of several experimental [1][2][3][4][5][6][7][8][9][10][11][12] and theoretical [13][14][15][16] studies over the last years. The rearrangement and fragmentation reactions involving this species have been explored by several experimental techniques: collisional activation, 1 mass spectrometry, 2,6,9 charge exchange, 10 and photoelectron-photoion coincidence (PEPI-CO).…”

“…The mercapto cation (CH 3 SH + ) has been the focus of several experimental [1][2][3][4][5][6][7][8][9][10][11][12] and theoretical [13][14][15][16] studies over the last years. The rearrangement and fragmentation reactions involving this species have been explored by several experimental techniques: collisional activation, 1 mass spectrometry, 2,6,9 charge exchange, 10 and photoelectron-photoion coincidence (PEPI-CO). 11 In the recent collisional activation experiment, 1 the C-S bond dissociation to form CH 3 + and SH was found to be the dominant product channel, even though this reaction channel is not among the energetically preferred pathways.…”

Lifetime of low vibrational levels of the metastableB̃2B2state ofH2O+<

“…The three lowest-lying electronic states of H 2 O + have been identified and investigated with photoelectron spectroscopy [25][26][27][28][29], photofragment spectroscopy [22,[30][31][32][33][34][35], as well as with photoelectron-photofragment coincidence spectroscopy [36][37][38] following vuv ionization or multiphoton ionization [22] of neutral water. Detailed spectroscopic studies have characterized the transitions between theà 2 A 1 and X 2 B 1 states, both via emission [23,24] and absorption [39][40][41][42][43] in the IR-visible (IR-VIS) region.…”

Electron-impact dissociation of H3O+

“…(e-+ AB+ _A + + B) (2) is often ignored, despite the fact that its cross section may be significantly larger2 for the electron energies ( > 5 eV) characteristic of excimer laser discharges. Studies of electronimpact dissociation ofHt show that3-6 for electron energies above 3 e V, dissociation has a larger cross section than dissociative recombination.…”