Zero-kinetic-energy (ZEKE) photoelectron spectroscopy of p-difluorobenzene via different intermediate vibrational levels in the S1 state

Self Cite

118

We investigate the low-energy transitions (0-570 cm -1 ) of the S1 state of para-fluorotoluene (pFT) using a combination of resonance-enhanced multiphoton ionization (REMPI) and zerokinetic-energy (ZEKE) spectroscopy and quantum chemical calculations. By using various S1states as intermediate levels, we obtain zero-kinetic-energy (ZEKE) spectra. The differing activity observed allows detailed assignments to be made of both the cation and S1 lowenergy levels. The assignments are in line with the recently-published work on toluene from the Lawrance group [J. Chem. Phys. 143, 044313 (2015)], which considered vibration-torsion coupling in depth for the S1 state of toluene. In addition, we investigate whether two bands that occur in the range 390-420 cm -1 are the result of a Fermi resonance; we present evidence for weak coupling between various vibrations and torsions that contribute to this region. This work has led to the identification of a number of misassignments in the literature, and these are corrected.2

Section: Zeke Spectrum Via S1 2d20supporting

confidence: 86%

Section: A Rempi Spectrummentioning

confidence: 85%

Section: Zeke Spectrum Via D20 M = 3(-)mentioning

confidence: 96%

See 1 more Smart Citation

Torsion and vibration-torsion levels of the S1 and ground cation electronic states of para-fluorotoluene

Gardner

Tuttle

Whalley

et al. 2016

Self Cite

118

“…Cation images are calibrated using photoelectron images of pDFB taken with identical voltage settings but with the polarity reversed. Zero kinetic energy ͑ZEKE͒ spectra of pDFB 30 are used to calibrate the photoelectron images.…”

Section: Methodsmentioning

confidence: 99%

The partitioning of energy amongst vibration, rotation, and translation during the dissociation of p-difluorobenzene–Ar neutral and cation complexes

Bellm

Lawrance

2003

The dissociation dynamics of p-difluorobenzene-Ar and p-difluorobenzene-Ar ϩ have been investigated from the 5 1 level in S 1 and the 29 2 level in D 0 , respectively. The technique of velocity map imaging has been used to determine the translational energy release distributions. In the case of 5 1 p-difluorobenzene-Ar, dispersed fluorescence spectra provide the distribution of vibrational energy in the p-difluorobenzene fragment. A significant fraction of the p-difluorobenzene products are formed in the 0 0 level. From the translational energy release data the rotational energy distribution within 0 0 can be inferred. The results show that the average rotational energy is 380 cm Ϫ1 , Ͼ5 times the average translational energy of 70 cm Ϫ1 . This rotational excitation infers that dissociation occurs with the Ar atom significantly displaced from its equilibrium position above the center of the aromatic ring. From the average rotational energy it is determined that the Ar atom is, on average, displaced by 1.8 -3.7 Å from the center of the aromatic ring at dissociation, i.e., the Ar atom is beyond the carbon atoms. In the case of dissociation from the 29 2 level of p-difluorobenzene-Ar ϩ , the vibrational distribution within the p-difluorobenzene ϩ product is not known, however it can be inferred from previous studies of dissociation within S 1 . As for the 5 1 p-difluorobenzene-Ar case, the evidence suggests that dissociation leads to significant rotational excitation of p-difluorobenzene ϩ . There are a limited number of destination vibrations within the p-difluorobenzene and p-difluorobenzene ϩ fragments for dissociation from 5 1 (S 1 ) and 29 2 (D 0 ), respectively. Hence there are only a few, widely separated, values for the combined translational and rotational energy available. Despite this, the translational energy release distributions in both cases are smooth and structureless. In the limit of no rotational excitation of the polyatomic fragment, the translational energy release distributions would show peaks only at energies corresponding to populated vibrational states of the product. The absence of such peaks indicates that rotational excitation of the product occurs for all vibrational states, reducing the average translational energy released and smearing the distribution.

“…For this reason, many studies have employed multiphoton ionization to study its spectroscopy and dynamics. [10][11][12] It is therefore important to understand the photoionization dynamics of p-DFB, particularly out of its S 1 ͑valence͒ electronic state in which a electron is ejected. In the D 2h point group, which is relevant to the equilibrium structure of p-DFB, there are two conventions commonly found in the literature which lead to different labeling of the irreducible representations, and thus different choices of the symmetry labels describing a͒ Present address: Atomic and Molecular Physics Laboratories, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia.…”

Section: Introductionmentioning

confidence: 99%

An unusual π* shape resonance in the near-threshold photoionization of S1 para-difluorobenzene

Bellm

Davies

Whiteside

et al. 2005

Previously reported dramatic changes in photoelectron angular distributions ͑PADs͒ as a function of photoelectron kinetic energy following the ionization of S 1 p-difluorobenzene are shown to be explained by a shape resonance in the b 2g symmetry continuum. The characteristics of this resonance are clearly demonstrated by a theoretical multiple-scattering treatment of the photoionization dynamics. New experimental data are presented which demonstrate an apparent insensitivity of the PADs to both vibrational motion and prepared molecular alignment, however, the calculations suggest that strong alignment effects may nevertheless be recognized in the detail of the comparison with experimental data. The apparent, but unexpected, indifference to vibrational excitation is rationalized by considering the nature of the resonance. The correlation of this shape resonance in the continuum with a virtual * antibonding orbital is considered. Because this orbital is characteristic of the benzene ring, the existence of similar resonances in related substituted benzenes is discussed.