Observation of the high-resolution infrared absorption spectrum of CO2 molecules isolated in solid parahydrogen

We report the observation of high-resolution (0.008 cm(-1)) infrared absorption spectra of CO2 molecules isolated in solid parahydrogen (pH(2)) matrices at T=2.4 to 4.8 K. Several extremely sharp (0.01 to 0.04 cm(-1) full-width-at-half- maximum) absorption features appear in the 2343.5 to 2345 cm(-1) region. We assign the three strongest peaks to the v(3) mode of isolated CO2 molecules. The spectra are consistent with trapping of the CO2 molecules in three distinct double-substitutional sites in hcp and fcc regions of the pH(2) solid. We offer several hypotheses as to the origins of the numerous weaker absorption features. (C) 2000 American Institute of Physics. [S1063-777X(00)00509-0].