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 absorp tion spectra of CO2 molecules isolated in solid parahydrogen (pH(2)) matric es at T=2.4 to 4.8 K. Several extremely sharp (0.01 to 0.04 cm(-1) full-wid th-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 molecule s in three distinct double-substitutional sites in hcp and fcc regions of t he pH(2) solid. We offer several hypotheses as to the origins of the numero us weaker absorption features. (C) 2000 American Institute of Physics. [S10 63-777X(00)00509-0].