Resonantly Enhanced Multiphoton Ionization and Zero Kinetic Energy Photoelectron Spectroscopy of Chrysene: A Comparison with Tetracene

Abstract

We report the electronic and vibrational spectroscopy of chrysene using resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. As an isomer of tetracene, chrysene contains a kink in the middle of the four fused hexagonal rings, which complicates not just the symmetry but, more importantly, the molecular orbitals and hence vibronic transitions. Incidentally, the two nearby electronically excited states of chrysene have the same symmetry, and vibronic coupling introduces no out-of-plane vibrational modes. As a result, the REMPI spectrum of chrysene contains essentially only in-plane ring deformation modes, similar to that of tetracene. However, density functional calculations using gaussian even after the inclusion of vibronic coupling can only duplicate the observed REMPI spectrum in a qualitative sense, and the agreement is considerably worse than our recent work on a few pericondensed polycyclic aromatic hydrocarbons and on tetracene. The ZEKE spectrum of chrysene via the origin band of the intermediate electronic state S(1), however, can be qualitatively reproduced by a straightforward Franck-Condon calculation. The ZEKE spectra from vibrationally excited states of the S(1), on the other hand, demonstrate some degree of mode selectivity: the overall intensity of the ZEKE spectrum can vary by an order of magnitude depending on the vibrational mode of the intermediate state. A scaling factor in the theoretical vibrational frequency for the cation is also needed to compare with the experimental result, unlike tetracene and pentacene.

Zero kinetic energy photoelectron spectroscopy of triphenylene

“…The value of the scaling factor is within the typical range for calculations using the B3LYP functional. [31][32][33][34][35][36][37] A feature of Gaussian 09 is inclusion of Herzberg-Teller coupling for simulations of vibronic transitions, often with very reasonable accuracy for intensity distributions. 45 The resulting spectrum can further assist with the assignment of the observed REMPI transitions.…”

“…However, a problem with Gaussian 09, regardless of methods of calculation, is the uncertainty in the energy of closely spaced excited electronic states. [31][32][33][34][35][36][37] Consequently in Figure 2, we show the simulated spectra with Herzberg-Teller coupling for both the S 1 ← S 0 and the S 2 ← S 0 transitions of triphenylene. Although the lack of an origin band could potentially complicate the assignment of the spectrum, fortunately in this case, the agreement between simulation and experiment in Figure 2 is quite reasonable.…”

“…This kind of internal energy "cutoff" seems typical for the ZEKE experiments that we have performed. [31][32][33][34][35][36][37] The inconsistent signal-to-noise ratio (S/N) of Fig. 4(c) is due to the extra effort in the scan of the central region (marked by two arrows): while the rest of the region and the rest of all the ZEKE spectra have been results of averages over 100 laser shots, this central region has been the average of 170 laser shots per data point.…”

“…30 In recent years, we have undertaken the mission of mapping out the low frequency vibrational modes of PAHs using ZEKE spectroscopy. [31][32][33][34][35][36][37] So far we have reported four pericondensed species including pyrene, benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), and benzo[g,h,i]perylene (BghiP) as well as three cata-condensed species including tetracene, pentacene, and chrysene. [31][32][33][34][35][36][37] Our results together with previous matrix isolation spectroscopy (MIS) [38][39][40][41] and other experimental efforts offer the possibility of a comprehensive analysis of the vibrational modes of a few selected cationic species, thereby benchmarking theoretical calculations and astrophysical modeling.…”

Electronic spectra and excited-state dynamics of acridine and its hydrated clusters

“…[28][29][30][31][32][33] The system is differentially pumped with a time-of-flight (TOF) mass spectrometer inside the detector chamber. The detection chamber is located inside the source chamber and is separated from the source chamber via a 2 mm diameter homemade skimmer and three extending arms.…”