15min:

XU WANG, SHENGGANG LI, JASON F. FULLER, PARAGRANJITA BHOWMIK, BRADFORD R. SOHNLEIN AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

A few years ago, a computational study was reported on cation- interactions in Al⁺ complexes with a series of aromatic compounds. However, for Al⁺(C₅H₅N), the calculations indicated that Al⁺ was -bound to the nitrogen in the ground electronic state. If Al⁺ was -bound to the ring, the potential energy surface was very flat and no minimum was located. Our photoelectron measurements on Al/Al⁺-pyridine vibrations agree with the theoretical predictions. The ground electronic states of Al⁺(C₅H₅N) and its neutral species were determined to be ¹A₁ and ²B₁ in C_2v symmetry. The aluminum-pyridine stretching frequencies were measured to be 278 cm^-1 in the ionic ¹A₁ state and 366 cm^-1 in the neutral ²B₁ state. It is unusual that the metal-ligand stretching frequency of a cation complex is much smaller than that of the corresponding neutral species. This anomaly will be discussed in terms of orbital and electrostatic interactions.