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Title: The study of state-selected ion-molecule reactions using thevacuum ultraviolet pulsed field ionization-photoion technique

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
COLLABORATION - Air Force Research Laboratory,MA
Sponsoring Org.:
USDOE Director. Office of Science. Basic EnergySciences
OSTI Identifier:
917825
Report Number(s):
LBNL-61737
R&D Project: 403101; BnR: KC0301020
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: The Journal of Chemical Physics; Journal Volume: 125; Related Information: Journal Publication Date: 10/04/2006
Country of Publication:
United States
Language:
English
Subject:
38

Citation Formats

Dressler, R.A., Chiu, Levandier, D.J., Tang, X.N., Hou, Y., Chang, C., Houchins, C., Xu, H., and Ng, Cheuk-Yiu. The study of state-selected ion-molecule reactions using thevacuum ultraviolet pulsed field ionization-photoion technique. United States: N. p., 2006. Web. doi:10.1063/1.2207609.
Dressler, R.A., Chiu, Levandier, D.J., Tang, X.N., Hou, Y., Chang, C., Houchins, C., Xu, H., & Ng, Cheuk-Yiu. The study of state-selected ion-molecule reactions using thevacuum ultraviolet pulsed field ionization-photoion technique. United States. doi:10.1063/1.2207609.
Dressler, R.A., Chiu, Levandier, D.J., Tang, X.N., Hou, Y., Chang, C., Houchins, C., Xu, H., and Ng, Cheuk-Yiu. Wed . "The study of state-selected ion-molecule reactions using thevacuum ultraviolet pulsed field ionization-photoion technique". United States. doi:10.1063/1.2207609.
@article{osti_917825,
title = {The study of state-selected ion-molecule reactions using thevacuum ultraviolet pulsed field ionization-photoion technique},
author = {Dressler, R.A. and Chiu and Levandier, D.J. and Tang, X.N. and Hou, Y. and Chang, C. and Houchins, C. and Xu, H. and Ng, Cheuk-Yiu},
abstractNote = {},
doi = {10.1063/1.2207609},
journal = {The Journal of Chemical Physics},
number = ,
volume = 125,
place = {United States},
year = {Wed Apr 12 00:00:00 EDT 2006},
month = {Wed Apr 12 00:00:00 EDT 2006}
}
  • This paper presents the methodology to generate beams of ions in single quantum states for bimolecular ion-molecule reaction dynamics studies using pulsed field ionization (PFI) of atoms or molecules in high-n Rydberg states produced by vacuum ultraviolet (VUV) synchrotron or laser photoexcitation. Employing the pseudocontinuum high-resolution VUV synchrotron radiation at the Advanced Light Source as the photoionization source, PFI photoions (PFI-PIs) in selected rovibrational states have been generated for ion-molecule reaction studies using a fast-ion gate to pass the PFI-PIs at a fixed delay with respect to the detection of the PFI photoelectrons (PFI-PEs). The fast ion gate provided bymore » a novel interleaved comb wire gate lens is the key for achieving the optimal signal-to-noise ratio in state-selected ion-molecule collision studies using the VUV synchrotron based PFI-PE secondary ion coincidence (PFI-PESICO) method. The most recent development of the VUV laser PFI-PI scheme for state-selected ion-molecule collision studies is also described. Absolute integral cross sections for state-selected H{sub 2}{sup +} ions ranging from v{sup +}=0 to 17 in collisions with Ar, Ne, and He at controlled translational energies have been obtained by employing the VUV synchrotron based PFI-PESICO scheme. The comparison between PFI-PESICO cross sections for the H{sub 2}{sup +}(HD{sup +})+Ne and H{sub 2}{sup +}(HD{sup +})+He proton-transfer reactions and theoretical cross sections based on quasiclassical trajectory (QCT) calculations and three-dimensional quantum scattering calculations performed on the most recently available ab initio potential energy surfaces is highlighted. In both reaction systems, quantum scattering resonances enhance the integral cross sections significantly above QCT predictions at low translational and vibrational energies. At higher energies, the agreement between experiment and quasiclassical theory is very good. The profile and magnitude of the kinetic energy dependence of the absolute integral cross sections for the H{sub 2}{sup +}(v{sup +}=0-2,N{sup +}=1)+He proton-transfer reaction unambiguously show that the inclusion of Coriolis coupling is important in quantum dynamics scattering calculations of ion-molecule collisions.« less
  • We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N{sub 2}{sup +}(v{sup +}, N{sup +}) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N{sub 2}{sup +}(X {sup 2}{Sigma}{sub g}{sup +}, v{sup +}= 0-2, N{sup +}= 0-9) PFI-PIs with high quantummore » state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N{sub 2}{sup +} PFI-PI beam can be formed with a laboratory kinetic energy resolution of {Delta}E{sub lab}={+-} 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E{sub cm}'s) down to thermal energies. Absolute total rovibrationally selected cross sections {sigma}(v{sup +}= 0-2, N{sup +}= 0-9) for the N{sub 2}{sup +}(X {sup 2}{Sigma}{sub g}{sup +}; v{sup +}= 0-2, N{sup +}= 0-9) + Ar CT reaction have been measured in the E{sub cm} range of 0.04-10.0 eV, revealing strong vibrational enhancements and E{sub cm}-dependencies of {sigma}(v{sup +}= 0-2, N{sup +}= 0-9). The thermochemical threshold at E{sub cm}= 0.179 eV for the formation of Ar{sup +} from N{sub 2}{sup +}(X; v{sup +}= 0, N{sup +}) + Ar was observed by the measured {sigma}(v{sup +}= 0), confirming the narrow {Delta}E{sub cm} spread achieved in the present study. The {sigma}(v{sup +}= 0-2; N{sup +}) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions calculated based on the Landau-Zener-Stueckelberg formulism are found to be in fair agreement with the present measured {sigma}(v{sup +}= 1 or 2; N{sup +}). Taking into account of the experimental uncertainties, the measured {sigma}(v{sup +}= 1 or 2, N{sup +}) for N{sup +}= 0-9 at E{sub cm}= 0.04-10.0 eV are found to be independent of N{sup +}.« less
  • By employing an electric field pulsing scheme for vacuum ultraviolet laser pulsed field ionization-photoion (PFI-PI) measurements, we have been able to prepare a rovibrationally selected PFI-PI beam of N{sub 2}{sup +}(v{sup +}= 1, N{sup +}) with not only high intensity and high quantum state purity, but also high kinetic energy resolution, allowing absolute total cross sections [{sigma}(v{sup +}= 1, N{sup +})] for the N{sub 2}{sup +}(X; v{sup +}= 1, N{sup +}) + Ar, N{sup +}= 0-8 charge transfer reaction to be measured at center-of-mass collision energies (E{sub cm}) down to thermal energies. The {sigma}(v{sup +}= 1, N{sup +}= 0-8) valuesmore » determined at E{sub cm}= 0.04-10.00 eV are in good agreement with the theoretical predictions based on the Landau-Zener-Stueckelberg formulism. Taking into account the experimental uncertainties, the {sigma}(v{sup +}= 1, N{sup +}), N{sup +}= 0-8, measured at E{sub cm}= 1.56 eV are found to be independent of N{sup +}.« less
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