Joost M. Bakker

The infrared absorption spectrum of the gas phase neutral benzoic acid monomer and dimer

The IR absorption spectrum of the jet-cooled benzoic acid monomer and dimer have been recorded throughout the 500–1900u2009cm−1 range via ion dip spectroscopy. Both spectra show a wealth of vibrational modes and the monomer spectrum is remarkably different from that of the dimer. Density functional theory calculations show quantitative agreement with the experimental data. The C–O–H out-of-plane bending vibration in the dimer is poorly reproduced in the theoretical calculations and a more accurate description of the doubly hydrogen bonded structure is therefore still needed.

Intensity-resolved IR multiple photon ionization and fragmentation of C60.

The sequential absorption of multiple infrared (IR) photons by isolated gas-phase species can lead to their dissociation and/or ionization. Using the newly constructed Free-Electron Laser for IntraCavity Experiments (FELICE) beam line at the FELIX facility, neutral C(60) molecules have been exposed to an extremely high number (approximately 10(23)) of photons/cm(2) for a total time duration of up to 5 micros. At wavelengths around 20 microm, resonant with allowed IR transitions of C(60), ionization and extensive fragmentation of the fullerenes are observed. The resulting photofragment distributions are attributed to absorption in fragmentation products formed once C(60) is excited to internal energies at which fragmentation or ionization takes place within the duration of the laser pulse. The high IR intensities available combined with the large interaction volume permit spatially resolved detection of the ions inside the laser beam, thereby disentangling the contributions from different IR intensities. The use of spatial imaging reveals intensity dependent mass distributions that are substantially narrower than what has been observed previously, indicating rather narrow energy distributions. A simple rate-equation modeling of the excitation process supports the experimental observations.

The infrared spectrum of the benzoyl cation

Abstract The vibrational spectrum of the gas phase benzoyl cation (C6H5CO+) in the 500–2500 cm −1 range is presented. Vapor phase benzoic acid is photolyzed/photoionized using an ArF excimer laser and the resulting ionic fragments are stored in a quadrupole ion trap. The benzoyl cation is subsequently isolated and its infrared spectrum is recorded through multiple photon dissociation spectroscopy with a free electron laser. Density functional calculations predict a C2v structure for the benzoyl cation, which is in good agreement with the observed spectrum.

Magnetic trapping of buffer-gas-cooled chromium atoms and prospects for the extension to paramagnetic molecules

We report the successful buffer-gas cooling and magnetic trapping of chromium atoms with densities exceeding 1012 atoms per cm3 at a temperature of 350 mK for the trapped sample. The possibilities of extending the method to buffer-gas cool and magnetically trap molecules are discussed. To minimize the most important loss mechanism in magnetic trapping, molecules with a small spin–spin interaction and a large rotational constant are preferred. Both the CrH (6Σ+ ground state) and MnH (7Σ+) radicals appear to be suitable systems for future experiments.