Low Temperature Physics: 26, 661 (2000); https://doi.org/10.1063/1.1312392 (8 pages)
Физика Низких Температур: Том 26, Выпуск 9-10 (Сентябрь 2000), c. 899-908    ( к оглавлению , назад )

Rovibrational transitions and nuclear spin conversion of methane in parahydrogen crystals

Masaaki Miki and Takamasa Momose

Division of Chemistry, Graduate School of Science, Kyoto University and Japan Science and Technology Corporation (JST), Kyoto 606-8502, Japan
E-mail: momose@kuchem.kyoto-u.ac.jp

Received February 7, 2000, revised May 25, 2000

Аннотация

Solid parahydrogen is an excellent matrix for matrix-isolation spectroscopy because of its high spectral resolution. Here, we describe rovibrational structure and the nuclear spin conversion of CH4 embedded in parahydrogen crystals studied by infrared absorption spectroscopy. The vibration-rotation absorptions of CH4 exhibit time-dependent intensity changes at 4.8 K. These changes are interpreted to be a result of the I=1→I=2 nuclear spin conversion which accompanies the J=1→J=0 rotational relaxation. The half-lifetime of the upper J=1 rotational state is unchanged by the addition of up to 2% orthohydrogen molecules, but decreases with more than 10% orthohydrogen molecules. The increase of the decay rate at higher orthohydrogen concentration indicates that the magnetic field gradient across CH4 caused by orthohydrogen molecules mixes the nuclear spin states which accelerate the conversion.

PACS:
33.20.Ea - Infrared spectra
33.70.√w -
82.20.Rp - State to state energy transfer (see also 31.70.Hq Time-dependent phenomena, and 34.50.Pi state-to-state scattering analyses-in atomic and molecular physics)