Vibrational energy transfer from CO to O2 in rare gas matrices.

Abstract

Abstract Vibrationally excited oxygen O2(ν) is produced in matrix isolated CO-O2 mixtures by IR laser excitation of 13C18O. The quenching of the CO Vibrational fluorescence by both 16O2 and 18O2 shows that energy transfer preferentially occurs from the high levels of CO. Laser probing of the vibrational energy contents of O2 confirms that a fraction of the energy initially deposited in CO is actually being converted into vibrational excitation of O2. Excitation spectra of the A' → X LIF reveal the existence of a broad O2(ν) distribution extending from ν = 4 to 20. Time resolved measurements show an extremely slow vibrational relaxation in O2. The 250 s lifetime of ν = 4 is the longest value ever reported for a molecular vibration in solids. The ν-dependence of the decay rates and their sensitivity to matrix change suggest that while vibrational relaxation of the lower levels is radiative in both Kr and Ar hosts, the upper levels are depopulated in the latter by radiationless multiphonon processes. Interstate cascading between O2(ν) and the nearby vibronic levels of the singlet manifolds is a negligible process. Quadrupolar effects are found to be important for both radiative relaxation and non-radiative energy transfer. The energy flow between the CO and O2 vibrational reservoirs is controlled by long-range dipole-quadrupole interactions. Vibrational up-pumping in O2 occurs through a sequence of CO2(ν) → O2(ν') transfer processes. In concentrated matrices back transfer from O2(ν) to ground state CO as well as quadrupole-quadrupole mediated fusion of O2(ν = 1) excitations compete with vibrational relaxation.