Nuclear Spin Symmetry Conservation and Relaxation in Water (1H216O) Studied by Cavity Ring-Down (CRD) Spectroscopy of Supersonic Jets
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- 作者：Carine Manca Tanner ; Martin Quack ; David Schmidiger
- 刊名：Journal of Physical Chemistry A
- 出版年：2013
- 出版时间：October 3, 2013
- 年：2013
- 卷：117
- 期：39
- 页码：10105-10118
- 全文大小：503K
- 年卷期：v.117,no.39(October 3, 2013)
- ISSN：1520-5215
文摘
We report high resolution near-infrared laser spectra of water seeded in a supersonic jet expansion of argon probed by cavity ring-down spectroscopy (CRDS) in the R branch of the 2谓3 band (above 7500 cm鈥?) at several effective temperatures T < 30 K. Our goal is to study nuclear spin symmetry conservation and relaxation. For low mole fractions of water in the gas mixture, we obtained the lowest rotational temperatures and observed nuclear spin symmetry conservation, in agreement with theoretical expectation for inelastic collisions of isolated H2O molecules with Ar and similar to a previous series of experiments with other small molecules in supersonic jet expansions. However, for the highest mole fractions of water, which we used (xH2O < 1.6%), we obtained slightly higher rotational temperatures and observed nuclear spin symmetry relaxation, which cannot be explained by the intramolecular quantum relaxation mechanism in the monomer H2O. The nuclear spin symmetry relaxation observed is, indeed, seen to be related to the formation of water clusters at the early stage of the supersonic jet expansion. Under these conditions, two mechanisms can contribute to nuclear spin symmetry relaxation. The results are discussed in relation to claims of the stability of nuclear spin isomers of H2O in the condensed phase and briefly also to astrophysical spectroscopy.