Millimeter-wave spectroscopy of H2=CCD: Tunneling splitting and ortho-para mixing interaction

Masato Hayashi, Kensuke Harada, Richard Lavrich, Takehiko Tanaka, Keiichi Tanaka

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The H2=CCD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0+ and 0-. Tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R - and two Q -branch transitions. Three and two pure rotational transitions in the Ka =0 and 1 stacks, respectively, were also observed for each of the 0+ and 0- states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be Δ E 0 =1187.234 (17) MHz, which is 1/14 that for H2 CCH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm -1, consistent with the value 1568 cm-1 obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δ aF (β) =68.06 (53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H2=CCD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H2=CCD.

Original languageEnglish
Article number154303
JournalJournal of Chemical Physics
Volume133
Issue number15
DOIs
Publication statusPublished - Oct 21 2010

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Charge coupled devices
Millimeter waves
millimeter waves
charge coupled devices
Spectroscopy
Ground state
spectroscopy
Ultraviolet lasers
Deuterium
Photolysis
interactions
Isomers
vinyl radical
Molecules
ground state
ultraviolet lasers
hyperfine structure
nuclear spin
deuterons
photolysis

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Millimeter-wave spectroscopy of H2=CCD : Tunneling splitting and ortho-para mixing interaction. / Hayashi, Masato; Harada, Kensuke; Lavrich, Richard; Tanaka, Takehiko; Tanaka, Keiichi.

In: Journal of Chemical Physics, Vol. 133, No. 15, 154303, 21.10.2010.

Research output: Contribution to journalArticle

Hayashi, Masato ; Harada, Kensuke ; Lavrich, Richard ; Tanaka, Takehiko ; Tanaka, Keiichi. / Millimeter-wave spectroscopy of H2=CCD : Tunneling splitting and ortho-para mixing interaction. In: Journal of Chemical Physics. 2010 ; Vol. 133, No. 15.
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abstract = "The H2=CCD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0+ and 0-. Tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R - and two Q -branch transitions. Three and two pure rotational transitions in the Ka =0 and 1 stacks, respectively, were also observed for each of the 0+ and 0- states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be Δ E 0 =1187.234 (17) MHz, which is 1/14 that for H2 CCH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm -1, consistent with the value 1568 cm-1 obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δ aF (β) =68.06 (53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H2=CCD are mixed up to about 0.1{\%}. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H2=CCD.",
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N2 - The H2=CCD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0+ and 0-. Tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R - and two Q -branch transitions. Three and two pure rotational transitions in the Ka =0 and 1 stacks, respectively, were also observed for each of the 0+ and 0- states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be Δ E 0 =1187.234 (17) MHz, which is 1/14 that for H2 CCH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm -1, consistent with the value 1568 cm-1 obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δ aF (β) =68.06 (53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H2=CCD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H2=CCD.

AB - The H2=CCD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0+ and 0-. Tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R - and two Q -branch transitions. Three and two pure rotational transitions in the Ka =0 and 1 stacks, respectively, were also observed for each of the 0+ and 0- states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be Δ E 0 =1187.234 (17) MHz, which is 1/14 that for H2 CCH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm -1, consistent with the value 1568 cm-1 obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δ aF (β) =68.06 (53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H2=CCD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H2=CCD.

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