Fast ortho-to-para conversion of molecular hydrogen in chemisorption and matrix-isolation systems.

Molecular hydrogen has two nuclear-spin modifications called and . Because of the symmetry restriction with respect to permutation of the two protons, the and isomers take only odd and even values of the rotational quantum number, respectively. The -to- conversion is promoted in condensed systems, to which the excess rotational energy and spin angular momentum are transferred.

Nuclear-spin conversion analysis of ν + ν combination band of crystalline methane in phase II.

We conducted reflection-absorption infrared spectroscopy in an ultrahigh vacuum and observed the ν + ν combination band of crystalline methane in phase II, where the rotating and librating species coexist. We analyzed the time- and temperature-dependence of the spectrum due to the nuclear-spin conversion of methane to update the assignment of the rotational and librational structure of this band. The conversion analysis performed in the present work will also be applicable to the detailed assignments of overtones and other combination bands.

Terahertz and mid-infrared spectroscopy of matrix-isolated clusters and matrix-sublimation ice of DO.

We have established an apparatus for terahertz and mid-infrared spectroscopy in an ultrahigh vacuum and have measured absorption spectra of DO clusters trapped in solid Ar. To assign terahertz absorption peaks due to the DO dimer, trimer, and tetramer, the dependence of the spectrum on the annealing temperature and DO dilution was analyzed. The assignment was also examined by ab initio calculations with the use of the "our own N-layered integrated molecular orbital and molecular mechanics" method, where the flexibility of surrounding Ar atoms was systematically incorporated.

Spectroscopic determination of interconversion rates among three nuclear spin isomers of methane in crystalline II.

We measured infrared absorption spectra of crystalline II of CH and succeeded in detecting a prominent Q(2) peak in the ν vibrational region by rapid cooling after annealing as well as previously reported rovibrational and librational-vibrational peaks. The integral intensities of the R(0), R(1), and Q(2) peaks were found to show biexponential dependence on time. This clearly demonstrates the interconversion among the three nuclear-spin isomers occupying low-lying rotational levels.

Asymmetric and symmetric absorption peaks observed in infrared spectra of CO2 adsorbed on TiO2 nanotubes.

Infrared spectra of CO2 physisorbed on titania nanotubes (TiNTs), predominantly in the anatase polymorph, were measured at 81 K. Asymmetric and symmetric absorption peaks due to the antisymmetric stretch vibration (ν3) of CO2 were observed at 2340 cm(-1) and 2350 cm(-1), respectively. On the basis of the exposure- and time-dependence of the spectrum, the 2340 cm(-1) peak was attributed to CO2 at the defective sites related to subsurface O vacancies (Vos) while the 2350 cm(-1) peak was assigned to that at the fivefold coordinated Ti(4+) sites.

Infrared spectroscopic investigation of nuclear spin conversion in solid CH4.

Infrared spectra of solid CH4 were studied in the ν3 and ν4 vibrational regions. The phase I crystal around 30 K showed broad absorption bands, whereas the phase II crystal at 6.9-10.