skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}

Abstract

Absolute measurements are presented for the excitation of the {nu}{sub 3} vibrational mode in CF{sub 4} by positron and electron impact from 0.1 to 2 eV. To minimize systematic differences, these measurements were made using the same trap-based electron or positron beam, associated experimental apparatus, and procedures. Unlike other vibrational excitation cross sections studied to date, the near-threshold cross section for the {nu}{sub 3} vibrational mode in CF{sub 4} is similar, both in magnitude and shape, for positrons and electrons. Comparison of the cross sections with an analytic Born dipole model yields good agreement, while comparison of this model with other measured positron-impact vibrational cross sections indicates that the contribution of this long-range dipole coupling varies widely. The maximum value of the cross section in CF{sub 4} is the largest of any positron-impact vibrational excitation cross section measured to date. This provides a likely explanation of the observation that CF{sub 4} is very effective when used as a buffer gas to cool positron gases and plasmas.

Authors:
;  [1]
  1. Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0319 (United States)
Publication Date:
OSTI Identifier:
20786301
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 72; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevA.72.062702; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CARBON TETRAFLUORIDE; COMPARATIVE EVALUATIONS; COUPLING; CROSS SECTIONS; DIPOLES; ELECTRON-MOLECULE COLLISIONS; ELECTRONS; ENERGY TRANSFER; EV RANGE; EXCITATION; PLASMA; POSITRON BEAMS; POSITRON-MOLECULE COLLISIONS; POSITRONS; TRAPS

Citation Formats

Marler, J. P., and Surko, C. M. Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}. United States: N. p., 2005. Web. doi:10.1103/PHYSREVA.72.0.
Marler, J. P., & Surko, C. M. Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}. United States. doi:10.1103/PHYSREVA.72.0.
Marler, J. P., and Surko, C. M. Thu . "Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}". United States. doi:10.1103/PHYSREVA.72.0.
@article{osti_20786301,
title = {Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}},
author = {Marler, J. P. and Surko, C. M.},
abstractNote = {Absolute measurements are presented for the excitation of the {nu}{sub 3} vibrational mode in CF{sub 4} by positron and electron impact from 0.1 to 2 eV. To minimize systematic differences, these measurements were made using the same trap-based electron or positron beam, associated experimental apparatus, and procedures. Unlike other vibrational excitation cross sections studied to date, the near-threshold cross section for the {nu}{sub 3} vibrational mode in CF{sub 4} is similar, both in magnitude and shape, for positrons and electrons. Comparison of the cross sections with an analytic Born dipole model yields good agreement, while comparison of this model with other measured positron-impact vibrational cross sections indicates that the contribution of this long-range dipole coupling varies widely. The maximum value of the cross section in CF{sub 4} is the largest of any positron-impact vibrational excitation cross section measured to date. This provides a likely explanation of the observation that CF{sub 4} is very effective when used as a buffer gas to cool positron gases and plasmas.},
doi = {10.1103/PHYSREVA.72.0},
journal = {Physical Review. A},
number = 6,
volume = 72,
place = {United States},
year = {Thu Dec 15 00:00:00 EST 2005},
month = {Thu Dec 15 00:00:00 EST 2005}
}
  • Using Fourier transform spectra recorded at 25 and 12 [mu]m, it has been possible to perform the first analysis of the 3[nu][sub 9] [minus] 2[nu][sub 9], 3[nu][sub 9] [minus] [nu][sub 5] and 3[nu][sub 9] [minus] [nu][sub 9] hot bands of HNO[sub 3] located at 392.4 cm[sup [minus]1], 409.8 cm[sup [minus]1], and 830.4 cm[sup [minus]1], respectively. An accurate description of the torsional splitting in the [nu][sub 9] = 3 vibrational state was achieved, leading to the determination of the two torsional band centers E[sub [nu][sub g]=3.1] = 1,288.8451 cm[sup [minus]1] and E[sub [nu][sub g]=3.2] = 1,288.9036 cm[sup [minus]1] and to themore » first determination of the [nu][sub 9] torsional potential of HNO[sub 3]. Finally, the 4[nu][sub 9] [minus] 3[nu][sub 9], [nu][sub 5] + [nu][sub 9] [minus] 2[nu][sub 9], and [nu][sub 5] + [nu][sub 9] [minus] [nu][sub 9] hot bands were identified for the first time at 375.3 [minus] 376.1 cm[sup [minus]1], 447.2 cm[sup [minus]1] and 885.424 cm[sup [minus]1] respectively.« less
  • Sequential pumping of the local OH stretch vibrations in hydrogen peroxide using infrared-optical double resonance permits spectroscopic access to the 4{nu}{sub OH}+{nu}{sub OH{prime}} combination level. Analysis of the rotationally resolved vibrational overtone spectra generated by this technique determines approximate rotational constants for this level and a value of 17 051.8{plus minus}3.4 cm{sup {minus}1} for the O--O bond dissociation energy. The linewidths of individual zeroth-order rotational transitions increase sharply with increasing {ital K} and change from smooth Lorentzian profiles to clumps of individual lines. The {ital K} dependence of the clump widths suggests that an {ital a}-axis Coriolis interaction is themore » primary coupling mechanism between the zeroth-order bright state and dark bath states. As a function of increasing {ital J}, each clump coalesces into a smooth Lorentzian profile. We interpret this {ital J} dependence in terms of a model that includes rotationally induced vibrational coupling among zeroth-order dark states.« less
  • Time-of-flight spectra for H/sup +/(D/sup +/)--CF/sub 4/ and SF/sub 6/ collisions have been measured with an improved resolution and at higher collision energies (10< or =E/sub lab/ < or =28 eV) compared to earlier work. In the low energy region (< or =13 eV) new distinct peaks are resolved for both molecules corresponding to small contributions from the second infrared active ..nu../sub 4/ mode in addition to the dominant ..nu../sub 3/ mode observed previously. Reexamination of experimental vibrational transition probabilities reveals an almost perfect agreement with a Poisson distribution for both modes up to the n = 6 overtone transitionmore » of ..nu../sub 3/. A simple straight line theory is used to calculate the energy transfer in small angle scattering from the long-range potential in good agreement with a full classical trajectory calculation. With this theory dipole moment derivatives can be determined directly from the observed energy transfers and are found to agree well with previous infrared measurements. At larger collision energies (> or =16 eV) an additional low intensity vibrational distribution is identified in the high energy loss tail of the spectra which can be attributed to small impact parameter collisions which probe the repulsive region of the potential. The observed energy transfers are also in good agreement with trajectory calculations indicating that the forced oscillator model is also applicable in the repulsive potential region for the present systems. A closer examination of the high energy loss tail reveals resolved structure which has been assigned to discrete states of the ..nu../sub 3/ mode in CF/sub 4/ up to the n = 14 overtone. These new results demonstrate that H/sup +/(D/sup +/) energy loss scattering can provide spectroscopic information not readily available from other experiments.« less
  • The fragmentation patterns of the halomethanes CCl{sub 2}F{sub 2}, CClF{sub 3}, CF{sub 4}, and CHF{sub 3} have been studied by positron impact, in the energy range from threshold to around 50 eV. These data were obtained using a quadratic potential time of flight mass spectrometer, coupled with a Penning trap and a LINAC-based positron source. The present data for positrons are compared with results for electron and photoionization from other works.
  • We present a study of dissociative electron attachment and vibrational excitation processes in electron collisions with the CF{sub 3}Cl molecule. The calculations are based on the two-dimensional nuclear dynamics including the C-Cl symmetric stretch coordinate and the CF{sub 3} symmetric deformation (umbrella) coordinate. The complex potential energy surfaces are calculated using the ab initio R-matrix method. The results for dissociative attachment and vibrational excitation of the umbrella mode agree quite well with experiment whereas the cross section for excitation of the C-Cl symmetric stretch vibrations is about a factor-of-three too low in comparison with experimental data.