Mass selective infrared spectroscopy using a free electron laser

Abstract

Mass selective gas-phase infrared spectroscopy using IR/VUV double resonance ionization is demonstrated. A free electron laser (FEL), tunable over the 100-2000 cm-~ range, is used as the IR excitation source while VUV light, produced by a F 2 laser, is used for subsequent ionization. Spectra are obtained by monitoring the ion of interest as a function of IR wavelength. It is shown that these spectra can give the same information as direct IR absorption spectra. The sensitivity of the method is many orders of magnitude higher than that of conventional IR absorption spectroscopy. First results on para amino benzoic acid (PABA) are presented.

The repopulation of electronic states upon vibrational excitation of niobium carbide clusters

“…In Ref. 32 it was demonstrated that a resonant IR excitation of para amino benzoic acid can lead to an enhanced UV photoionization yield at frequencies below the ionization threshold. As there are no possible electronically excited states within a few eV of the ground state, the excitation must be purely vibrational, and the enhancement due to an efficiency increase of the ionization probability, presumably simply by the increase of possible ionization pathways.…”

“…As there are no possible electronically excited states within a few eV of the ground state, the excitation must be purely vibrational, and the enhancement due to an efficiency increase of the ionization probability, presumably simply by the increase of possible ionization pathways. We test whether the same could be true for Nb 3 C 2 by modeling the gain as the ratio of the number of accessible ionization channels from the thermally populated vibrational densities of states (vDOS) 32,33 , considering all transitions from the populated vDOS to the continuum. In this treatment we do not take into account (unknown) differences in the Franck-Condon factors and assume that the transition probabilities from all the vibrational levels to the continuum are equal.…”

Infrared multiple photon dynamics and spectroscopy of cationic PABA and its dehydroxylated fragment ion

“…Its jet-cooled UV spectrum was recorded over PCCP www.rsc.org/pccp a decade ago. 24 Recently, the gas-phase infrared spectra of cationic aniline 25 and benzoic acid, 26 as well as that of neutral PABA, 27 were investigated with the use of an FEL. To our knowledge, no infrared spectra have to date been reported for the PABA cation nor for the PABz cation.…”

Vibrational spectroscopy of neutral silicon clusters via far-IR-VUV two color ionization

“…The high sensitivity of such an approach has been demonstrated for para-amino benzoic acid using a free electron laser as a tunable radiation source in the midinfrared range, where other intense lasers are lacking. 29 We here apply such an IR-UV two color ionization scheme for obtaining the vibrational spectra of neutral silicon clusters in the far-IR range between 225 and 550 cm −1 . These results constitute a͒ Electronic mail: fielicke@fhi-berlin.mpg.de.…”