5 research outputs found
Recommended from our members
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 Sâ. From the simulated REMPI spectra with and without HerzbergâTeller coupling, we conclude that vibronic coupling plays a minor but observable role in the electronic excitation to the Sâ state. We further compare the Sâ state of BhQ with the first two electronically excited states of phenanthrene, noticing a similarity of the Sâ state of BhQ with the second electronically excited state Sâ of phenanthrene. In the ZEKE spectra of BhQ, the vibrational frequencies of the cationic state Dâ 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 Sâ and Dâ states. We speculate that the nitrogen atom can withdraw an electron in the Sâ state and donate an electron in the Dâ state, thereby minimizing the structural change during ionization. The origin of the first electronically excited state is determined to be 29âŻ410 ± 5 cmâ»Âč, and the adiabatic ionization potential is determined to be 65âŻ064 ± 7 cmâ»Âč
Recommended from our members
Zero kinetic energy photoelectron spectroscopy of triphenylene
We report vibrational information of both the first electronically excited state and the ground
cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton
ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited
electronic state Sâ of the neutral molecule is of Aâ' symmetry and is therefore electric dipole forbidden
in the Dââ group. Consequently, there are no observable Franck-Condon allowed totally
symmetric aâ' vibrational bands in the REMPI spectrum. All observed vibrational transitions are
due to Herzberg-Teller vibronic coupling to the E' third electronically excited state Sâ. The assignment
of all vibrational bands as e' symmetry is based on comparisons with calculations using
the time dependent density functional theory and spectroscopic simulations. When an electron is
eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to Câᔄ
and resulting in two nearly degenerate electronic states of Aâ and Bâ symmetry. Here we follow
a crude treatment by assuming that all e' vibrational modes resolve into bâ and aâ modes in the
Câᔄ molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic
ionization threshold is determined to be 63 365 ± 7 cmâ»Âč. The observed ZEKE spectra contain
a consistent pattern, with a cluster of transitions centered near the same vibrational level of the
cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete
assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much
more extensive calculations, which will be performed in the future
Recommended from our members
Resonantly enhanced multiphoton ionization and zero kinetic energy photoelectron spectroscopy of Benzo[e]pyrene
We report zero kinetic energy (ZEKE) photoelectron spectroscopy via resonantly enhanced multiphoton ionization (REMPI) for benzo[e]pyrene. Extensive vibronic coupling between the first electronically excited state and a nearby state allows bâ symmetric modes to be observed which would normally be Franck-Condon (FC) disallowed. These vibronic modes are comparable in intensity to the FC allowed aâ modes. Gaussian 09 is able to qualitatively simulate the vibronic spectra of the REMPI and the ZEKE experiment using density functional methods. The ZEKE spectra demonstrate propensity in preserving the vibrational excitation of the intermediate electronic state. These results suggest a remarkable structural stability of BeP in accommodating the additional charge.Keywords: far infrared vibrational spectroscopy, photoionization spectroscopy, zero kinetic energy photoelectron spectroscopy, vibronic coupling, polycyclic aromatic hydrocarbon