No abstract

By using the technique of mass-analyzed threshold ionization spectroscopy, we were able to measure ionization energies of indole−Ar (62505 cm-1), indole−H2O (59433 cm-1), and the indole−benzene (59833 cm-1) complexes, as well as their dissociation energies in the cationic ground state. The dissociation energies in the neutral ground state are calculated from the experimental data. The ionic E 0 = 537 ± 10 cm-1 and neutral dissociation energy D 0 = 451 ± 15 cm-1 of the indole−Ar complex are much smaller than those of the indole−H2O complex; E 0 = 4790 ± 10 cm-1, D 0 = 1632 ± 15 cm-1 and of the indole−C6H6 complex:  E 0 = 4581 ± 10 cm-1, D 0 = 1823 ± 15 cm-1. This demonstrates the van der Waals character of the indole−Ar complex and the hydrogen bonding type in indole−water. Furthermore, we conclude that the indole−benzene complex is hydrogen-bonded with the benzene π-cloud serving as electron donator and indole serving as hydrogen donator.

No abstract

Delayed pulsed field threshold ionization of clusters excited to high long-lived Rydberg states is used to study their dissociation behavior. Benzene–Ar and benzene–Kr dimers are excited by resonance enhanced two-photon ionization to Rydberg levels close to various ionization thresholds. The field ionized threshold ions are monitored and separated from the non-energy-selected ions in a reflecting field mass spectrometer with high mass resolution. The appearance of threshold ions at the daughter ion mass indicates the onset of a dissociation process. Daughter ions are first observed for the 16161(3/2) level of the two investigated dimers. This leads to an upper limit of the dissociation energy of benzene–Ar of 340 cm−1 which is probably higher than the true dissociation energy. For the first time threshold ions are observed for large internal energies of some 5 eV in the core indicating that high Rydberg states maintain their long lifetime even if the core is electronically or vibrationally excited by several eV.

No abstract

High-resolution state-selected ion-molecule reaction studies using pulsed field ionization photoelectronsecondary ion coincidence method Rev. Sci. Instrum. 74, 4096 (2003); Absorption spectroscopy of massselected ions in neon matrices

High resolution laser excitation was combined with the technique of mass-selected two-photon ionization via aresonant intermediate state to measure rotationally resolved UV spectra of benzene-Ar van der Waals clusters. When the second laser pulse in the two color experiment is delayed by 7 ns no line broadening due to the second ionizing absorption step is observed. Spectra of three vibronic bands in the SI +-So transition ofbenzene (h 6 )-Ar and benzene (d 6 )-Ar were measured yielding a line spectrum with a linewidth of 130 MHz. Resolution is sufficient to demonstrate that no asymmetry splitting of the rotationallines occurs and the spectrum is to a high precision that of a symmetrie rotor. A detailed analysis ofthe rotational structure yields an accurate set ofrotational constants. We find that the Ar is located on the C 6 rotational axis. Its distance from the benzene ring plane is 3.582 A in the electronic ground state and decreases by 59 ± 3 mA in the electronically excited state due to the increased polarizability of the benzene moleeule after electronic excitation.

Articles you may be interested inPulsed-field ionization spectroscopy of high Rydberg states ( n = 50 -200 ) of bis( η 6 -benzene)chromium Adiabatic and vertical ionization energies of 1,4-diazabicyclo[2,2,2]-octane measured by zero electron kinetic energy spectroscopy and Rydberg extrapolation Structure and vibrations of dihydroxybenzene cations and ionization potentials of dihydroxybenzenes studied by mass analyzed threshold ionization and infrared photoinduced Rydberg ionization spectroscopy as well as ab initio theoryResolved high Rydberg spectroscopy of benzenerare gas van der Waals clusters: Enhancement of spin-orbit coupling in the radical cation by an external heavy atom