Desorption Dynamics, Internal Energies, and Imaging of Organic Molecules from Surfaces with Laser Desorption and Vacuum Ultraviolet (VUV) Photoionization

Photoionization Spectroscopy of Nucleobases and Analogues in the Gas Phase Using Synchrotron Radiation as Excitation Light Source

“…In an "Arrhenius-like" behavior, the amount of internal energy can be deduced totally from the activation barrier, leading to a red shift of the AE that can be easily observed. For example, in the work of Gaie-Levrel et al [10], a red shift of 0.57 AE 0.1 eV is observed for the formation of m/z 130 from the dissociative photoionization of tryptophan when raising the temperature of the hot finger, used for the aerosol vaporization, from 423 to 558 K. An observed AE red shift can in turn be used to deduce E int by assuming that the latter is approximated by a collection of harmonic oscillators, as has been done in [47,48]. In this context, one has to calculate vibrational frequencies of the molecule by theoretical chemistry methods.…”

“…Very recently, pulsed laser desorption was successfully used in combination with tunable (and continuous) VUV-SR, although the duty cycle of laser/synchrotron light interaction is unfavorable [5,6,48]. In these challenging experiments, the desorption and ionization processes are separated in space (and thus in time, since the desorbed molecules need to travel to the center of the ion source).…”

“…Using this technique, Zhou et al also presented photoionization efficiency (PIE) spectra for the amino acid α-alanine. The experimental approach of Kostko et al [48] is quite different from that of Zhou et al [6]. Indeed, Kostko et al used an Nd:YLF laser emitting at λ ¼ 349 nm and operating at a repetition rate of 2.5 kHz for desorption.…”

“…This kind of mass spectrometer is normally operated using ion sputtering with fast, pulsed ion beams of nanosecond duration and several keV kinetic energy. Kostko et al [48] were thus able to measure PI mass spectra of A, T, C, and U NABs. In their work, the laser desorption dynamics are studied and it is found that the internal temperature of laser-desorbed thymine is about 800 K whereas its translational temperature is well below, ranging from 216 to 346 K for the four NABs under study.…”

“…This aspect has been studied in depth in [10,[46][47][48] and the literature cited therein. The amount of internal energy E int imparted to the neutral upon vaporization is important to know for gas phase electronic spectroscopic studies of large molecules like NABs, since it directly affects their tautomer/conformer/rotamer distribution.…”