High-resolution Photoabsorption Spectroscopy Research Articles

Electronic excitation of furfural as probed by high-resolution vacuum ultraviolet spectroscopy, electron energy loss spectroscopy, and ab initio calculations.

The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.

Toluene Valence and Rydberg Excitations as Studied by ab initio Calculations and Vacuum Ultraviolet (VUV) Synchrotron Radiation.

The electronic spectroscopy of isolated toluene in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 4.0-10.8 eV energy range, with absolute cross-section measurements derived. We present the first set of ab initio calculations (vertical energies and oscillator strengths), which we use in the assignment of valence and Rydberg transitions of the toluene molecule. The spectrum reveals several new features not previously reported in the literature, with particular relevance to 7.989 and 8.958 eV, which are here tentatively assigned to the π*(17a') ← σ(15a') and 1π*(10a″) ← 1π(14a') transitions, respectively. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of toluene in the upper stratosphere (20-50 km).

Electronic states of tetrahydrofurfuryl alcohol (THFA) as studied by VUV spectroscopy and ab initio calculations.

The electronic spectroscopy of isolated tetrahydrofurfuryl alcohol (THFA) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.0-10.8 eV energy-range, with absolute cross-section measurements derived. The He(I) photoelectron spectrum was also collected to quantify ionization energies in the 9-16 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground and excited state of the positive ion. The good agreement between the theoretical results and the measurements allows us to quantify for the first time the electronic-state spectroscopy of THFA. The present work also considers the question of the lowest energy conformers of the molecule and its population distribution at room temperature.

Iodopentafluorobenzene: Electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption and photoelectron spectroscopy

The electronic transitions of iodopentafluorobenzene (C 6F 5I) have been investigated experimentally for the first time by high-resolution photoabsorption spectroscopy in the energy range 3.6–10.7 eV. The character of the valence excited states has been discussed taking into account calculations available in the literature. The ionisation energies of the molecule in its electronic ground state have been measured by high-resolution He(I) photoelectron spectroscopy. The energies of the ionic bands are shifted by about 0.5 eV compared to the earliest literature values but they agree with the most recently published measurements. All the spectra presented in this paper represent highest resolution measurements of their kind for iodopentafluorobenzene. The absolute photoabsorption cross-sections have been used to model photolysis rates and residence times in the terrestrial atmosphere.

Electronic states of neutral and ionized tetrahydrofuran studied by VUV spectroscopy and ab initio calculations

The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8–10.6 eV with absolute cross-section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10° over the 5–11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9–16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature.

Electronic spectroscopy of bromopentafluorobenzene by high-resolution vacuum ultraviolet photoabsorption, electron impact, and photoelectron spectroscopies

The electronic transitions of bromopentafluorobenzene (C6F5Br) have been investigated by high-resolution photoabsorption spectroscopy in the energy range 4–10.8eV. In addition, the electron energy loss spectrum (EELS) was recorded in non-strictly electric dipolar interaction conditions (40eV incident energy, 10° scattering angle) over the range 4–13.0eV. The present spectra provide the first experimental data on the electronic states of bromopentafluorobenzene. The characteristics of the electronic excited states are discussed and the terrestrial atmospheric photolysis rates have been derived from the absolute photoabsorption cross-sections. The ionisation energies of the occupied molecular orbitals have been measured by high-resolution He(I) photoelectron spectroscopy, allowing a precise value of 9.679±0.002eV to be derived for the ionic ground state.

Electronic State Spectroscopy of c-C5F8 Explored by Photoabsorption, Electron Impact, Photoelectron Spectroscopies and Ab Initio Calculations

The electronic transitions and resonance-enhanced vibrational excitations of octafluorocyclopentene (c-C5F8) have been investigated using high-resolution photoabsorption spectroscopy in the energy range 6-11 eV. In addition, the high-resolution electron energy loss spectrum (HREELS) was recorded under the electric dipolar excitation conditions (100 eV incident energy, approximately 0 degrees scattering angle) over the 5-14 eV energy loss range. A He(I) photoelectron spectrum (PES) has also been recorded between 11 and 20 eV, allowing us to derive a more precise value of (11.288 +/- 0.002) eV for the ground neutral state adiabatic ionization energy. All spectra presented in this paper represent the first and highest resolution data yet reported for octafluorocyclopentene. Ab initio calculations have been performed for helping in the assignment of the spectral bands for both neutral excited states and ionic states.

K-shell excitation of the water, ammonia, and methane molecules using high-resolution photoabsorption spectroscopy.

The K-shell excitation spectra of the hydrides water, ammonia, and methane have been measured in photoabsorption experiments using synchrotron radiation in combination with a high-resolution monochromator. For the case of methane, in particular, a wealth of spectral detail is observed which was not accessible in previous studies. The measured excitation energies and relative intensities compare well with values calculated using a complete second-order approximation for the polarization propagator. In order to determine the extent of admixing of valence excitations (i.e., transitions into virtual ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ orbitals) to the Rydberg manifolds, the X-H bond lengths have been varied in the calculations. In the case of ${\mathrm{H}}_{2}$O, the two lowest-energy bands are due to the O 1s-4${\mathit{a}}_{1}$/3s and O 1s-2${\mathit{b}}_{2}$/3p transitions and have strong valence character; their width indicates that both excitations are dissociative. The ${\mathrm{NH}}_{3}$ and ${\mathrm{ND}}_{3}$ spectra are also broad which is not only due to possible dissociation but also to unresolved vibrational fine structure (${\ensuremath{\nu}}_{2}$ mode) and a Jahn-Teller instability. Valence character is concentrated in the lowest excited state in the Rydberg ns manifold, but is distributed more uniformly over the np(e) manifold. The weak dipole-forbidden C 1s-3s(${\mathit{a}}_{1}$) transition in ${\mathrm{CH}}_{4}$ and ${\mathrm{CD}}_{4}$ is accompanied by vibrational structure due to the ${\ensuremath{\nu}}_{4}$ mode, indicating that it derives its intensity from vibronic coupling with the C 1s-3p(${\mathit{t}}_{2}$) transition. The structure on the latter band is extremely complicated due to Jahn-Teller coupling and cannot be assigned at present, as is the case for the Rydberg transitions at higher energies. The higher np Rydberg excitations contain considerable valence character.

High resolution photoabsorption spectroscopy at the carbonK-Edge

Using plane grating, ellipsoidal mirror, grazing incidence monochromators at the storage ring BESSY, a resolution of ≦ 150meV was achieved for a photon energy of 285 eV. This high energy resolution considerably extends the range of possible studies using core level Spectroscopy. Some of the new opportunities are illustrated at the CK edge by resolving the vibrational fine structure of condensed C2H4 multilayers in the (1s−1, π*) state by means of photoabsorption spectroscopy. For the sake of comparison with other high resolution instruments, the vibrational fine structure of condensed N2 multilayers at the NK edge (∼ 400eV) was also measured, yielding a resolving power of 3000.