Julia A. Davies

VUV optical absorption and electron energy-loss spectroscopy of ozone

Absolute VUV optical absorption cross sections for ozone have been measured between 325 and 110 nm (3.0 - 11.3 eV) using a synchrotron radiation source. Vibrational fine structure is resolved in Rydberg bands and comparison of this with the limiting bands in the photoelectron spectrum confirms that the order (increasing ionization energy) of the three lowest ionization bands is . Near-threshold electron energy-loss spectra have also been recorded. In these, in addition to the known triplet states between 1 and 2 eV, a low-lying triplet state has been located around 3.4 eV and several others between 6 and 9 eV. Characterization of the valence states (both optically allowed and forbidden) are discussed in relation to the results of early theoretical computations which seem to give a good account of the ozone spectrum.

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

K.L.R. acknowledges EPSRC for funding Grant Nos. GR/M83759 and GR/R72297, including postdoctoral support for J.A.D. and S.M.B.

The 700-1500 cm−1 region of the S1 (Ã1B2) state of toluene studied with resonance-enhanced multiphoton ionization (REMPI), zero-kinetic-energy (ZEKE) spectroscopy, and time-resolved slow-electron velocity-map imaging (tr-SEVI) spectroscopy

We report (nanosecond) resonance-enhanced multiphoton ionization (REMPI), (nanosecond) zero-kinetic-energy (ZEKE) and (picosecond) time-resolved slow-electron velocity map imaging (tr-SEVI) spectra of fully hydrogenated toluene (Tol-h8) and the deuterated-methyl group isotopologue (α3-Tol-d3). Vibrational assignments are made making use of the activity observed in the ZEKE and tr-SEVI spectra, together with the results from quantum chemical and previous experimental results. Here, we examine the 700-1500 cm(-1) region of the REMPI spectrum, extending our previous work on the region ≤700 cm(-1). We provide assignments for the majority of the S1 and cation bands observed, and in particular we gain insight regarding a number of regions where vibrations are coupled via Fermi resonance. We also gain insight into intramolecular vibrational redistribution in this molecule.

Study of electronically excited states of ozone by electron‐energy‐loss spectroscopy

Electronically excited states of ozone have been studied by electron‐energy‐loss spectroscopy. Two broad bands without visible vibrational structure are observed at 1.8±0.2 eV and 2.05±0.05 eV under scattering conditions favoring singlet excitation, that is a scattering angle of ϑ=10° and residual energy Er=20 eV. The lower is assigned as 1A2, the higher as 1B1 (Chappuis band). Bands with rich vibrational structure are observed under scattering conditions favoring triplet excitation, ϑ=30°–135° and residual energy Er=1–3 eV. At least two vibrational progressions can be discerned. The first has an origin at 1.30 eV, the origin of the second cannot be determined unambiguously, it is either at 1.53 or 1.45 eV. The well‐known Hartley band and a number of other singlet and triplet excited states are observed at higher energy losses. Excitation functions and angular distributions of the triplet band at 1.30 eV and of the Hartley band are presented. The absolute value of the differential cross section for excita...

Photoelectron spectroscopy of S1 toluene: II. Intramolecular dynamics of selected vibrational levels in S1 toluene studied by nanosecond and picosecond time-resolved photoelectron spectroscopies

We present results which suggest that the photophysics of S(1) toluene is significantly more complicated than that of the related molecules p-fluorotoluene or p-difluorobenzene. We have measured a range of photoelectron spectra for a number of S(1) internal energies, on different time scales and at different temperatures, in an attempt to unravel the competing processes, but the final conclusion remains outstanding.

Production of vibrationally autodetaching in low-energy electron impact on ozone

Attachment of electrons with energies of 1.2 to 2 eV to ozone was found to lead to the production of O and vibrationally excited , the latter subsequently lose electrons by vibrational autodetachment. This type of electron scattering is intermediate between inelastic electron scattering and dissociative attachment. Spectra of the detached electrons have resolved vibrational structure, which can be assigned to the individual vibronic transitions, providing detailed information on the product state distribution. The absolute integral cross section for the production of in vibrational states was found to be substantial, for example at 1.7 eV it is (with an error bar of about and ). Measurements of the signal onsets permit an independent determination of the dissociation energy of ozone into O and with the result eV. Comparison of the peak width of the electrons detached by in this work with the width of peaks of resonances observed in electron- scattering indicates a moderate degree of rotational excitation in the present process.

Picosecond pump–probe photoelectron spectroscopy as a probe of intramolecular dynamics in S1 para-fluorotoluene

Picosecond photoelectron spectroscopy is used to monitor the intramolecular dynamics in S1 parafluorotoluene prepared with ∼1200 cm−1 of internal energy from a jet cooled sample. The spectra evolve dramatically over a 100 ps timescale supporting results from chemical timing experiments. This suggests that initial temperature has little effect on the energy redistribution rate.

Differential oscillator strengths for chlorine dioxide, OClO, produced by electron impact energy-loss spectroscopy

Electron impact spectroscopy has been used for the first time to obtain energy-loss spectra for chlorine dioxide, OClO, over an energy range 2.5 to 12.5 eV. The differential oscillator strength (DOS) obtained from the energy-loss spectrum is compared with the DOS obtained from optical measurements. Oscillator strengths for several transitions have been calculated from a summation of the DOS and comparisons are also made with previous optical data.

Vibrational excitation of ozone by electron impact

The first measurements of electron impact vibrational excitation of ozone are presented as a function of both incident electron energy, 3 eV<or=Ei<or=7 eV, and scattering angle, 40 degrees <or= theta <or=120 degrees . Evidence is given for the formation of a low-lying shape resonance at Ei approximately=4 eV. Preliminary vibrational excitation cross sections are also presented.

Complex and Sustained Quantum Beating Patterns in a Classic IVR System: The 3(1)5(1) Level in S1 p-Difluorobenzene.

Using picosecond time-resolved photoelectron imaging, we have studied the intramolecular vibrational energy redistribution (IVR) dynamics that occur following the excitation of the 3(1)5(1) level, which lies 2068 cm(-1) above the S1 origin in p-difluorobenzene. Our technique, which has superior time resolution to that of earlier studies but retains sufficient energy resolution to identify the behavior of individual vibrational states, enables us to determine six distinct beating periods in photoelectron intensity, only one of which has been observed previously. Analysis shows that the IVR dynamics are restricted among only a handful of vibrational levels, despite the relatively high excitation energy. This is deduced to be a consequence of the high symmetry and rigid structure of p-difluorobenzene.