Search

The low-frequency stretching and bending vibrations of the isotopologues CH 2 D + , CD 2 H + and CD 3 + have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions CD m H n + + H 2 → h ν CD m - 1 H n + 1 + + HD have been applied for these species. As this scheme is not applicable to CH 3 + , the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting CH 3 + - He spectrum, broad features are observed below 1000 cm - 1 possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations.

The gas phase vibrational spectrum of CH3CNH+ is investigated using a messenger infrared predissociation (IRPD) action spectroscopic method. Vibrational bands were recorded in the 300-1700 cm−1 and 2000-3300 cm−1 regions making use of the widely tunable free electron laser for infrared experiments, FELIX, coupled to a cryogenic ion trap instrument. Band assignments were aided by high-level quantum-chemical calculations, which showed excellent agreement with the experimental data. Effects of the neon atom used as messenger in the IRPD method are investigated in detail. The data presented here will support astronomical searches for the CH3CNH+ ion in space, and provide a basis for high-resolution ro-vibrational and pure rotational studies in vibrationally excited states.

Electro-optic (EO) detection of relativistic Coulomb fields offers a method for non-destructive longitudinal profile measurements of ultrashort bunches. Techniques for single-shot EO characterisation of Coulomb fields which have been developed or demonstrated at the FELIX free electron laser (FEL) facility are discussed. In addition, recent FELIX experiments have used single-shot electro-optic detection to measure the temporal profile of the far-infrared electric field pulse of coherent synchrotron radiation (CSR), initial results of which are reported here. Such time-resolved CSR measurements have the potential for a completely non-invasive bunch longitudinal profile determination, without the ambiguity in profile that is present in CSR spectral measurements.

We present 2-color pump/probe experiments on the sensory protein Photoactive Yellow Protein (PYP). We present a snapshot of the transient IR spectrum of PYP at 100 ps after the pump pulse, in the important amide I and amide II region around 6 μm .

A study of infrared laser-induced desorption of N 2 O condensed on NaCl(1 0 0) is presented. The comparison of the wavelength dependent desorption yield to the linear absorption spectrum shows that desorption of intact molecules occurs at the resonance frequencies of the symmetric stretching and the bending vibration of N 2 O. The analysis of the time-of-flight spectra yields translational temperatures that are well above the substrate temperature and depend strongly on the applied laser fluence. In addition, the dependence of the desorption signal on layer thickness and substrate temperature is investigated. The results are discussed in the context of different desorption mechanisms, and it is concluded that a resonant heating process can best explain the experimental observations.