Issue 17, 2004

Is the ESR spectrum attributable to H2 or H2+(H2)2? Precise measurement of the g-value and anisotropic hyperfine structure in γ-irradiated solid parahydrogen

Abstract

Four ESR lines, found by Miyazaki et al. in 1995 in irradiated solid parahydrogen (ca. 92% para-purity) at 4.2 K, assigned as “H2,” were precisely re-measured with highly pure solid parahydrogen (>99.9%) and compared with calculated g-value and hyperfine coupling constants of H2+(H2)2. The g-value of I,MI = 0,0 feature, reported previously as 2.0033 or 2.0023, was found to be incorrect and has now been corrected to 2.002120 ± 0.000012. This corrected value is clearly smaller than that of free electron. We also found that the remaining three lines corresponding to I,MI = 1,0; 1, +1; and 1, –1 features have axially symmetric hyperfine anisotropic structure i.e., A = 20.318 and A = 20.502 mT. This anisotropy corresponds to the rotation of the species in solid parahydrogen. Although the experimental g-value and isotropic hyperfine coupling constants are in good agreement with those of H2+(H2)2 estimated by ab initio calculation, it is still difficult to explain why H2+ (H2)2 clusters turned into ESR inactive species by addition of 0.1∼1% D2 in the present system. In this regard, we still maintain that the species in solid parahydrogen are H2.

Article information

Article type
Paper
Submitted
23 Feb 2004
Accepted
02 Jun 2004
First published
24 Jun 2004

Phys. Chem. Chem. Phys., 2004,6, 4363-4368

Is the ESR spectrum attributable to H2 or H2+(H2)2? Precise measurement of the g-value and anisotropic hyperfine structure in γ-irradiated solid parahydrogen

J. Kumagai, M. Hanabusa, H. Inagaki and S. Kariya, Phys. Chem. Chem. Phys., 2004, 6, 4363 DOI: 10.1039/B402756F

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