| AVS 60th International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | N. Ozawa, Gakushuin University, Japan |
| Authors: | N. Ozawa, Gakushuin University, Japan S. Takekuma, Gakushuin University, Japan K. Yamakawa, Gakushuin University, Japan I. Arakawa, Gakushuin University, Japan |
| Correspondent: | Click to Email |
Water clusters have been investigated in terms of their geometric structures and electronic states for the last few decades [1]. One of the main purposes of these studies was to obtain information of hydrogen-bond interactions in water and ice. Experimentally, a matrix isolation technique, in which water clusters are prepared in a condensed film of chemically inactive species such as para-H2, and rare gases, has also been a useful method for the cluster study because of high sample density [2][3]. It is worth noting that the cyclic water hexamer which has not been found in the gas phase was observed in para-H2 matrices [4]. In the present study we investigated water clusters in the methane matrix by Fourier Transform Infrared Spectroscopy (FTIRS).
A vacuum chamber equipped with a liquid helium cryostat was evacuated and baked at 393 K for 24 hours, which resulted in the base pressure of 1 * 10-8 Pa. The methane matrix was deposited on the gold-coated oxygen-free copper substrate which was fixed on the cryostat and maintained at 6 K. Methane and water vapor were dosed from different gas lines through variable leak valves. The mole ratios of water to methane (H2O/CH4) were 0.026-0.053. Infrared spectra were measured in a reflection configuration using a FTIR spectrometer with a compartment of a liquid nitrogen cooled HgCdTe detector. The spectral range was 500-6000 cm-1 and a resolution was set at 4 cm-1 in the present experiment. The incident angle of infrared light on the substrate was 80 . The whole optical path was evacuated to eliminate infrared absorption due to carbon dioxide and water vapor in the atmosphere.
The infrared spectra of water clusters in methane matrices showed adsorption peaks at 3531 cm-1, 3497 cm-1, 3360 cm-1, 3344 cm-1 and 3216 cm-1, all of which are attributed to vibrational modes of bonded OH, which forms a hydrogen bond with an oxygen atom of a neighboring water molecule. The peaks at 3531 cm-1 and 3497 cm-1 are due to the trimer and the peak at 3216 cm-1 to the cage-hexamer. The other peaks at 3360 cm-1 and 3344 cm-1 may be attributed to pentamer and cyclic-hexamer, respectively. In addition to the variety of the absorption peaks, we found that the relative intensities of these peaks depended on the H2O/CH4 ratio, which was likely to reflect the size distribution of the water clusters.
[1] A. Bankura et al., Chem. Phys. 400, 154 (2012).
[2] M. E. Fajardo et al., J. Chem. Phys. 115, 6807 (2001).
[3] S. Hirabayashi et al., J. Chem. Phys. 122, 244501 (2005).
[4] F.Huisken et al., J. Chem. Phys. 104, 17 (1996).