Theoretical and infrared spectroscopic investigation of the O2-•benzene and O4-•benzene complexes

The infrared spectra of the O-2(-)center dot benzene and O-4(-)center dot benzene complexes are determined by means of Ar predissociation spectroscopy. Several transitions due to CH stretch fundamentals and various combination bands are observed in the 2700-3100 cm(-1) region. The experimental results are interpreted with the aid of electronic structure calculations. A comparison of the calculated and experimental spectra reveals that the spectrum of O-2(-)center dot benzene most likely arises from an isomer where the superoxide molecule binds preferentially to one CH group of benzene. In contrast, the spectrum of O-4(-)center dot benzene yields a CH pattern remarkably similar to that displayed by the C-2 nu X-center dot benzene (X=halogen) complexes, consistent with a structure with two CH groups equally involved in the bonding. The lower energy vibrational fundamental transitions of the O-4(-) anion are recovered with a slight redshift in the O-4(-)center dot benzene spectrum, establishing that this charge-delocalized dimer ion retains its identity upon complexation. (c) 2007 American Institute of Physics.