Detailed measurements employing a combination of a cryogenic flowing afterglow with Langmuir probe (Cryo-FALP II) and a stationary afterglow with near-infrared absorption spectroscopy (SA-CRDS) show that binary electron recombination of para-H3(+) and ortho-H3(+) ions occurs with significantly different rate coefficients, (p)αbin and (o)αbin, especially at very low temperatures. The measurements cover temperatures from 60 K to 300 K. At the lowest temperature of 60 K, recombination of para-H3(+) is at least three times faster than that of ortho-H3(+) ((p)αbin=(1.8±0.4)×10(-7) cm(3) s(-1) vs. (o)αbin=(0-0 (+5))×10(-8) cm(3) s(-1)).
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http://dx.doi.org/10.1063/1.4927094 | DOI Listing |
Faraday Discuss
July 2019
Faculty of Mathematics and Physics, Department of Surface and Plasma Science, Charles University, V Holešovičkách 2, 180 00 Praha 8-Libeň, Czech Republic.
We present studies on the thermalisation of H3+ ions in a cold He/Ar/H2 plasma at temperatures 30-70 K. We show that we are able to generate a rotationally thermalised H3+ ensemble with a population of rotational and nuclear spin states corresponding to a particular ion translational temperature. By varying the para-H2 fraction used in the experiment we are able to produce para-H3+ ions with fractional populations higher than those corresponding to thermodynamic values.
View Article and Find Full Text PDFJ Chem Phys
July 2015
Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, Prague 18000, Czech Republic.
Detailed measurements employing a combination of a cryogenic flowing afterglow with Langmuir probe (Cryo-FALP II) and a stationary afterglow with near-infrared absorption spectroscopy (SA-CRDS) show that binary electron recombination of para-H3(+) and ortho-H3(+) ions occurs with significantly different rate coefficients, (p)αbin and (o)αbin, especially at very low temperatures. The measurements cover temperatures from 60 K to 300 K. At the lowest temperature of 60 K, recombination of para-H3(+) is at least three times faster than that of ortho-H3(+) ((p)αbin=(1.
View Article and Find Full Text PDFJ Phys Chem A
October 2013
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, United States.
The fundamental molecular ion H3(+) has impacted astronomy, chemistry, and physics, particularly since the discovery of its rovibrational spectrum. Consisting of three identical fermions, its properties are profoundly influenced by the requirements of exchange symmetry, most notably the nonexistence of its ground rotational state. Spectroscopy of H3(+) is often used to infer the relative abundances of its two nuclear spin modifications, ortho- and para-H3(+), which are important in areas as diverse as electron dissociative recombination and deuterium fractionation in cold interstellar clouds.
View Article and Find Full Text PDFJ Chem Phys
June 2012
Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, Prague 18000, Czech Republic.
Measurements in H(3)(+) afterglow plasmas with spectroscopically determined relative abundances of H(3)(+) ions in the para-nuclear and ortho-nuclear spin states provide clear evidence that at low temperatures (77-200 K) para-H(3)(+) ions recombine significantly faster with electrons than ions in the ortho state, in agreement with a recent theoretical prediction. The cavity ring-down absorption spectroscopy used here provides an in situ determination of the para/ortho abundance ratio and yields additional information on the translational and rotational temperatures of the recombining ions. The results show that H(3)(+) recombination with electrons occurs by both binary recombination and third-body (helium) assisted recombination, and that both the two-body and three-body rate coefficients depend on the nuclear spin states.
View Article and Find Full Text PDFPhys Rev Lett
May 2011
Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic.
Utilizing different ratios of para to ortho H₂ in normal and para enriched hydrogen, we varied the population of para-H₃⁺ in an H₃⁺ dominated plasma at 77 K. Absorption spectroscopy was used to measure the densities of the two lowest rotational states of H₃⁺. Monitoring plasma decays at different populations of para-H₃⁺ allowed us to determine the rate coefficients for binary recombination of para-H₃⁺ and ortho-H₃⁺ ions: (p)α(bin)(77 K) = (1.
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