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Title: Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues

Authors:
; ; ;
Publication Date:
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1375556
Grant/Contract Number:
DEAC52- 06NA25396
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review A
Additional Journal Information:
Journal Volume: 96; Journal Issue: 2; Related Information: CHORUS Timestamp: 2017-08-18 19:34:12; Journal ID: ISSN 2469-9926
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Scarlett, Liam H., Zammit, Mark C., Fursa, Dmitry V., and Bray, Igor. Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues. United States: N. p., 2017. Web. doi:10.1103/PhysRevA.96.022706.
Scarlett, Liam H., Zammit, Mark C., Fursa, Dmitry V., & Bray, Igor. Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues. United States. doi:10.1103/PhysRevA.96.022706.
Scarlett, Liam H., Zammit, Mark C., Fursa, Dmitry V., and Bray, Igor. 2017. "Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues". United States. doi:10.1103/PhysRevA.96.022706.
@article{osti_1375556,
title = {Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues},
author = {Scarlett, Liam H. and Zammit, Mark C. and Fursa, Dmitry V. and Bray, Igor},
abstractNote = {},
doi = {10.1103/PhysRevA.96.022706},
journal = {Physical Review A},
number = 2,
volume = 96,
place = {United States},
year = 2017,
month = 8
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on August 18, 2018
Publisher's Accepted Manuscript

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  • In this work we report the observation of polyatomic high-Rydberg molecules which survive for several hundred microseconds. Methane and ethane were excited by electron impact to produce high-Rydberg states of their fragments: CH/sub 3/ from methane and CH/sub 3/, C/sub 2/H/sub 4/, and C/sub 2/H/sub 5/ from ethane. These identifications are proven by measurements of threshold energies and by comparisons to fragmentation patterns for dissociative ionization. Sharp threshold peaks in the excitation functions show the occurrence of direct high-l excitation. The absence of parent CH/sub 4/ or C/sub 2/H/sub 6/ in high-Rydberg states remains unexplained, but may be related tomore » a strong interaction between the Rydberg electron and the core.« less
  • Electron impact dissociation of CH/sub 4/, C/sub 2/H/sub 4/, and C/sub 2/H/sub 6/ produces high Rydberg H and C fragments. Time-of-flight measurements and excitation functions help to characterize the molecular processes involved. Although details differ, the three molecules display similar dissociation behavior; relatively low kinetic energy fragments (< or approx =8 eV) arise from states between 19 and 30 eV, higher kinetic energy fragments from states between 30 and 40 eV (states most likely with doubly ionized cores), and even higher kinetic energy fragments (up to 18 eV) from states above 40 eV. Comparisons of high Rydberg kinetic energy spectramore » with available ion kinetic energy spectra show general agreement confirming the utility of the core ion model for polyatomic molecules.« less
  • The dissociation of CO caused by 1-MeV/amu F[sup 4+] impact has been studied using the coincidence time-of-flight technique. The kinetic energy released during the dissociation of CO[sup [ital Q]+] into ion pairs C[sup [ital q]][sub 1]+ and [ital O][sup [ital q]][sub 2][sup +] was determined from the measured difference in the times of flight of the two charged fragments. The kinetic-energy distributions of CO[sup 2+] dissociating into C[sup +] and O[sup +] as a result of different impinging projectiles have been compared. These distributions shift towards higher kinetic-energy release values with increasing strength of interaction. A single Gaussian kinetic-energy distributionmore » is in good agreement with the highly charged CO dissociation, while for doubly and triply charged CO, additional Gaussians are needed. While the Coulomb-explosion model approximately predicts the most likely value of a measured distribution, the widths of all distributions are grossly underestimated by the model. The measured widths of the distributions can be explained only by invoking the existence of potential-energy curves of the multiply charged ions that have steeper and shallower slopes as compared to the Coulombic curve. The reflection method was used to calculate the kinetic-energy release for F[sup 4+]+CO[r arrow]CO[sup 2+*] transitions to all known CO[sup 2+] states. The final kinetic-energy distribution was then fitted to the data in order to evaluate the weights of the different transitions. The calculated fit is in fair agreement with the measured one, although the high-energy tail of the measured distribution could not be accounted for, indicating that contributions from highly excited dissociating states or from curve crossings need to be included.« less
  • The production of high-Rydberg (HR) atomic fragments by electron-impact dissociation of 13 molecules has been compared to the results of previous work on the production of HR rare gas atoms. Measurements have been made of principal quantum number distributions, effective radiative lifetimes, and excitation cross sections including both the shapes as a function of electron-impact energy and the absolute magnitudes. Principal quantum number (n) distributions peak at lower n values than those for the rare gases and are consistent with the shorter times of flight of dissociation fragments. The HR atomic fragments appear to form in high angular momentum (l)more » states as a direct result of the dissociation process, whereas rare gas atoms form initially in low-l HR states and require subsequent electron collisions to reach high-l HR states. The energy dependence of the excitation cross sections, a slow rise from threshold with a peak near 100 eV, resembles that of other dissociative excitation processes and does not display the step function threshold characteristic of the rare gases. Magnitudes of the excitation cross sections are expressed in a form which separates the apparatus-dependent radiative decay factor from the initial excitation cross section. The result permits calculation of HR densities under a variety of electron-impact dominated conditions.« less