Energy transfer involving higher excited states: a comparison between CO …anthracene and O2 …anthracene in Ar matrices

Excitation energy transfer (EET) has been observed to occur from CO to anthracene, a polycyclic aromatic hydrocarbon, in Ar matrices (CO: Ar = 1 : 1000) at 18 K. In spite of the fact that the excitation energy available in CO (7.927 eV or above) is higher than the ionization threshold of anthracene (7.47 eV), emission from neutral anthracene between 360 and 500 nm has been observed when CO has been excited between 157 and 120 nm using synchrotron radiation. This electronic-to-electronic EET occurs through a nonradiative resonant process as well as the radiative reabsorption of UV emission of CO by anthracene. Under the same conditions, even at a one order of magnitude higher concentration of O2, no radiative processes of any kind that may result from an EET between O2 and anthracene could be observed.