The ionisation energy of cyclopentadienone: a photoelectron–photoion coincidence study

Abstract

Imaging photoelectron photoion coincidence (iPEPICO) spectra of cyclopentadienone (C 5 H 4 =O and C 5 D 4 =O) have been measured at the Swiss Light Source Synchrotron (Paul Scherrer Institute, Villigen, Switzerland) at the Vacuum Ultraviolet (VUV) Beamline. Complementary to the photoelectron spectra, photoionisation efficiency curves were measured with tunable VUV radiation at the Chemical Dynamics Beamline at the Advanced Light ). For both experiments, molecular beams diluted in argon and helium were generated from the vacuum flash pyrolysis of o-phenylene sulphite in a resistively heated microtubular SiC flow reactor. The Franck-Condon profiles and ionisation energies were calculated at the CCSD(T) level of theory, and are in excellent agreement with the observed iPEPICO spectra. The ionisation energies of both cyclopentadienone-d 0 , IE(C 5 H 4 =O), and cyclopentadienoned 4 , IE(C 5 D 4 =O), were observed to be the same: 9.41 ± 0.01 eV. The mass-selected threshold photoelectron spectrum (ms-TPES) of cyclopentadienone reveals that the C=C stretch in the ground state of the cation is excited upon ionisation, supporting computational evidence that the ground state of the cation is X + 2 A 2 , and is in agreement with previous studies. However, the previously reported ionisation potential has been improved considerably in this work. In addition, since o-benzoquinone (o-O=C 6 H 4 =O and o-O=C 6 D 4 =O) is also produced in this process, its ms-TPES has been recorded. From the iPEPICO and photoionisation efficiency spectra, we infer an adiabatic ionisation energy of IE(o-O=C 6 H 4 =O) = 9.3 ± 0.1 eV, but the rather structureless spectrum indicates a strong change in geometry upon ionisation making this value less reliable.

Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: a combined neutral and distonic radical study

“…S1 and S2, respectively). The PI onsets for m/z 80 at 9.4 eV and m/z 108 at 9.2 eV are in agreement with reference spectra for cyclopentadienone (CPO, m/z 80) and o-benzoquinone (o-BQ, m/z 108), [53][54][55] and consistent with AIEs provided in Table 1. Ionization onsets for CPO and o-BQ were recently reported by Ormond et al 53 and compared within the inset of Fig.…”

The Threshold Photoelectron Spectrum of Fulvenone: A Reactive Ketene Derivative in Lignin Valorization

“…It is worth comparing theX þ 2 A 2 part of ms-TPES of fulvenone to that of cyclopentadienone. [23] It is not surprising that similar vibrational features are observed in both compounds, as the ionization takes place from basically the same a 2 HOMO, which is purely located at the cyclopentadiene moiety.…”

Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol

“…Further decomposition of the C 5 H 4 OH radical leads to H-atom and to the well characterized48,[74][75][76][77] cyclopentadienone, C 5 H 4 =O (m/z 80).Fig. 5 is the 118.2 nm PIMS that is observed when a sample of catechol is heated in a pulsed, 1 mm SiC micro-reactor.…”