Photoelectron spectroscopy of 7-azaindole–water cluster anions

Abstract.

The 7-azaindole (7-AzI) cluster anions and their H₂O adducts were generated by electron attachment to the 7-AzI/7-AzI–H₂O clusters, and their electronic properties studied with mass spectrometry and photoelectron spectroscopy. In the mass spectra of the 7-AzI cluster anions, (7-AzI) _n ^-, monomer anions were missing due to negative electron affinity (EA), while clusters (n≥2) have positive EA, and those having even n were more abundant than those at odd n. EA increased with cluster size from 0.88 eV at n=2, and an even–odd alternation in the EA was seen. The even–odd alternation showed that the 7-AzI dimer acts as a unit for cluster formation. In the photoelectron spectrum of (7-AzI)₂ ^- at 266 nm, the second peak was observed 2.4 eV above the first peak; this is attributed to the triplet state of the neutral (7-AzI)₂. Depending on the detachment energy, a movable peak, with the detachment of 420–300 nm (2.9–4.1 eV), was additionally observed between the first and the second peaks; this was thought to be caused by a delayed photoemission via an electronic excited state of the (7-AzI)₂ ^- anion.