High-resolution PIRSS using a tunable diode laser: the multiple of the collective v2 bending vibration of the p(2 × 1) monolayer CO 2 adsorbed on NaCl(001)

Abstract

Polarization infrared surface spectroscopy (PIRSS) has been used to investigate the multiplet of the collective v 2 bending vibration of the p(2 × 1) monolayer CO 2 adsorbed on NaCl(001) in the spectral range 650–665 cm −1 at temperatures between 10 and 90 K. Tunable diode laser spectroscopy with a resolution of at least 5 × 10 −3cm −1 appears to be a powerful method to study the lineshape of extremely narrow absorptions observed for highly ordered adsorbates on insulator single crystal surfaces. The experiments have been performed in transmission geometry with a lead salt laser diode. Four polarized absorptions are expected in the spectral range of the bending vibration of CO 2 adsorbed on NaCl(001) at monolayer coverage due to the combination of site symmetry and correlation field splitting. They have been observed and studied in detail using four different laser modes. The continuously tunable range of a single mode is limited to about 3 cm −1. All spectra have been recorded as a function of temperature. In the low-temperature limit, linewidths down to 0.04 cm −1 have been observed, the bands being clearly asymmetric. One of the observed quartet components shows an unexpected doublet splitting under the extremely high resolution employed.