Knowledge Bank

The 3400 {\AA} singlet-triplet band system in benzene and in benzene-$d6$, perturbed by the presence of oxygen, has been investigated in absorption in the vapor phase at room temperature using pathlengths up to 400 meters with oxygen pressures up to 2 atmospheres and over a 6 cm. path with oxygen pressures up to 140 atmospheres. The effect of deuteration is to displace the system to higher energy by about $180cm-1$ and to decrease the frequency of the totally symmetric vibration $(\nu 2)$ by $40\pm 10cm-1$. Some additions to the previously reported vibrational structure have been found, although the band profile appears to be constant over the range of pressures used. The intensity of the bands has been investigated as a function of both oxygen and benzene pressures, and is found to depart significantly from the direct proportionality which had been assumed previously. A discussion of this departure will be given. No evidence was found to support the idea of a stable benzene-oxygen complex.