A photoionization mass spectrometric and threshold photoelectron-photoion coincidence study of vinylbromide (C2H3Br) in the vacuum ultraviolet range of 6–21eV

Abstract

The dissociative photoionization of vinyl bromide (C 2 H 3 Br) has been investigated by photoionization mass spectrometry (PIMS) and time-of-flight threshold photoelectronphotoion coincidence (TOF-TPEP-ICO) spectrometry using synchrotron radiation. The photoionization efficiency curves of the three most abundant ions, i.e. C 2 H 3 Br + , C 2 H 3 + and C 2 H 2 + , are measured and analyzed in detail. A C 2 H 3 + /Br -photoion-pair formation process has been detected for the first time. Some arguments are provided in favor of the electronic excitation of the C 2 H 3 + fragment and of the isomerization of the C 2 H 2 + ions. The breakdown diagram for these ions in the 9.8-21 eV photon energy range, derived from TOF-TPEPICO mass spectra, is discussed. The involvement of the successive C 2 H 3 Br + ionic states and the role of autoionization of C 2 H 3 Br Rydberg states are emphasized. For the two minor HBr + and Br + fragment ions only the breakdown diagrams are measured and appearance energies are derived.

Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy

“…The ionicà state has been implicated with respect to the C-Br bond dissociation in a previous study involving single photon ionization. 68 The relevant energetics for dissociative ionization and ionic dissociation are 68 C 2 H 3 Br → C 2 H 3 + Br + 15.4 eV,…”

“…66 This result is similar to the results of photoelectron-photoion coincidence experiments, which showed that vinyl bromide parent ions with sufficient energy to dissociate yielded only C 2 H 3 + +Br ( 2 P 3/2 ) products. 67,68…”

Ultrafast dynamics of cationic electronic states of vinyl bromide by strong-field ionization-photofragmentation

“…Figure 3 shows the vertical transition energies (VTE) of the electronic states of C 2 H 3 Br cation, along with the appearance energies (AE) of the dissociation channels, which were reported in previous PIMS and TPEPICO study using synchrotron radiation. [27] At low SFI-laser energy, the electron is more likely to be ionized from the molecular HOMO, and the parent ions are in the ground state X 2 A according to the Koopmans' theorem. After the PF-laser is introduced, the cations are resonantly excited from X 2 A to the C 2 A state, as it lies at a vertical transition energy that is equal to onephoton energy of the 400 nm laser (hν 400 nm = 3.1 eV).…”

“…Previous studies have investigated the dissociation channels of C 2 H 3 Br + using the photoionization mass spectrometry (PIMS) and the threshold photoelectron-photoion coincidence (TPEPICO) techniques. [27] The breakdown diagram for C 2 H 3 Br + , C 2 H + 3 , and C 2 H + 2 ions by synchrotron radiation in the photon energy of 9.8-21 eV was discussed. [27] Compared to synchrotron radiation, femtosecond laser could provide time-resolved measurements on femtosecond time scale, which is capable of resolving the ultrafast evolution of the molecular ionic excited states.…”

“…[27] The breakdown diagram for C 2 H 3 Br + , C 2 H + 3 , and C 2 H + 2 ions by synchrotron radiation in the photon energy of 9.8-21 eV was discussed. [27] Compared to synchrotron radiation, femtosecond laser could provide time-resolved measurements on femtosecond time scale, which is capable of resolving the ultrafast evolution of the molecular ionic excited states. Recently, the NIR-XUV transient absorption spectroscopy experiment demonstrated that the C 2 H + 3 + Br ( 2 P 3/2 ) dissociation channel occurs on the cationic A 2 A state with a time of 330 ± 150 fs.…”