화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.119, No.50, 11997-12004, 2015
Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline
We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[h]quinoline (BhQ) via resonantly enhanced multiphoton ionization (REMPI) through the first electronically excited state S-1. From the simulated REMPI spectra with and without Herzberg-Teller coupling, we conclude that vibronic coupling plays a minor but observable role in the electronic excitation to the S-1 state. We further compare the S-1 state of BhQ with the first two electronically excited states of phenanthrene, noticing a similarity of the S-1 state of BhQ with the second electronically excited state S-2 of phenanthrene. In the ZEKE spectra of BhQ the vibrational frequencies of the cationic state D-0 are consistently higher than those of the intermediate neutral state, indicating enhanced bonding upon ionization. The sparse ZEKE spectra, compared with the spectrum of phenanthrene containing rich vibronic activities, further imply that the nitrogen atom has attenuated the structural change between S-1 and D-0 states. We speculate that the nitrogen atom can withdraw an electron in the S-1 state and donate an electron in the D-0 state, thereby minimizing the structural change during ionization. The origin of the first electronically excited state is determined to be 29 410 +/- 5 cm(-1), and the adiabatic ionization potential is determined to be 65 064 +/- 7 cm(-1).