JET-COOLED SOLVENT COMPLEXES WITH INDOLES

Cold mass-resolved excitation spectra have been obtained for substitut ed and unsubstituted indoles complexed with one or two polar solvent m olecules. Frequency scans were carried out to more than 1000 cm(-1) ab ove the complex origins. Sharp excitation features persisted to the bl ue for the N-H site complexes, but no features further to the blue wer e attributable to the pi site complexes. In 3-methylindole a number of vibrations 400-900 cm(-1) above the SI origin in the bare chromophore did not appear in corresponding locations above the Sl complex origin s for n = 1 water and methanol clusters. It is likely that these peaks underwent much greater red shifts in the complexes than the S-1 origi ns because the former possess substantial (1)L(a), character. Any of t he indoles studied that was complexed with two polar solvent molecules showed broad excitation features. The extended structure most likely arises in at least some instances because of pi site interactions. In 2,3-dimethylindole, postulated to undergo N-H bond dissociation in S-1 , mass-resolved REMPI spectra did not disclose a lower mass product ar ising from N-H bond breaking. However, when the chromophore was comple xed at the N-H site with a strong proton acceptor, triethylamine, evid ence was found that zwitterions were formed in the S-1 complex arising from N-H site proton donation to the base.