CO2 in Solid Para-Hydrogen: Spectral Splitting and the CO2•••(o-H2)n Clusters

Complicated high-resolution spectral structures are often observed for molecules doped in solid molecular hydrogen. The structures can result from miscellaneous effects and are often interpreted differently in references. The spectrum of the nu(3) band of CO2 in solid para-H-2 presents a model system which exhibits rich spectral structures. With the help of the potential energy simulation of the CO2 molecule doped in para-hydrogen matrix, and extensive experiments with different CO2 isotopologues and different ortho-hydrogen concentrations in the matrix, the spectral features observed in p-H-2 matrix are assigned to the CO2 center dot center dot center dot(o-H-2)(n) clusters and also to energy level splitting that is due to different alignments of the doped CO2 molecules in the matrix. The assignments are further supported by the dynamics analysis and also by the spectrum recorded with sample codoped with O-2 which serves as catalyst transferring o-H-2 to p-H-2 in the matrix at 4K temperature. The observed spectral features of CO2/pH(2) can potentially be used as an alternative readout of the temperature and orthohydrogen concentration in the solid para-hydrogen.