High-resolution spectroscopy of HCI and DCI isolated in solid parahydrogen: Direct, induced, and cooperative infrared transitions in a molecular quantum solid

摘要

The infrared spectroscopy and rovibrational dynamics of HCl and DCl dopants in solid parahydrogen (pH_2) were investigated using high-resolution spectroscopic methods. The absorption spectra of HCl and DCl monomers in solid pH_2 closely resemble the corresponding low temperature gas phase spectra, indicating that the gas phase vibrational and rotational quantum numbers of the dopant are conserved within the pH_2 solid. Small deviations from gas phase behavior are observed, however, such as a reduced HCl rotational energy level spacing and splitting of hte fivefold orientational degeneracy of HCl rotational states with J=2. In addition, the pure vibrational Q_1(0) (v=1<-0, J=0<-0) H_2 transition, which is infrared inactive in pure solid pH_2, is detected in the HCl doped sample. We propose that this transition is nduced in pH_2 molecules by neighboring HCl molecules through a weak "overlap induction" mechanism that is the only induction mechanism operative for J=0 impurities in pH_2. Rovibrational transtions are also detected near the induced Q_1(0) H_2 absorption; these are attributed to cooperative transition involving single photon excitation of pH_2-HCl pairs. Detailed isotopic analysis revelas that these cooperative transitions involve pure vibrational excitation of the pH_2 and pure rotational excitation of the HCl. Two-molecule transitions have long been studied for isotopic and rotational dopants (e.g., D_2, HD, orthohydrogen) in solid pH_2, but this is the first time such cooperative transitions have been attributed to a chemical impurity in pH_2 matrices.