Time-of-flight investigation of infrared laser-induced multilayer desorption of benzene

Abstract

Infrared (IR) laser-induced resonant desorption/ablation of benzene layers condensed on liquid-nitrogen-cooled substrates has been investigated using the time-of-flight (TOF) technique. Adsorbates of up to 5 μm thickness were irradiated with a line-tuned TEA CO2 laser. Time-resolved detection of desorbed particles was performed with a quadrupole mass spectrometer (QMS). Measured TOF spectra can usually be well fitted with a stream-modified Maxwell–Boltzmann distribution. Systematic deviations from these fits were observed depending on film thickness, laser fluence, and angle of detection. Spectroscopic data of the adsorbate–substrate system needed for model calculations were measured in situ. The absorption coefficients were found to be fluence dependent. Measurements of the desorption yield and kinetic energy of the desorbed particles were performed with the P932 and P934-CO2 laser lines as a function of film thickness and laser fluence. The solid–liquid phase transition could clearly be observed in these experiments. Average kinetic energies of up to 0.8 eV were measured in the TOF spectra, where the adsorbate temperature could be estimated to be less than 600 K. IR multilayer laser-induced desorption (LID) exhibits features very similar to those reported for UV multilayer LID. A mechanism based on the sudden rise of the adsorbate vapor pressure due to fast energy deposition by the laser pulse is discussed.

Computer Simulations of Laser Ablation of Molecular Substrates

“…The resulting concentration of the tensile stresses can be sufficient to separate the dynamic part of the computational cell from the rigid layer. Although the simulations with rigid boundary condition can be related to experiments performed for a thin absorbing organic layer deposited on a substrate, 23 in most cases we are interested in much larger systems for which the effect of the substrate can be neglected.…”

Velocity distributions of analyte molecules in matrix-assisted laser desorption from computer simulations

“…[3][4][5] Using two fitting parameters of the distribution, namely, the temperature and the stream velocity of the plume, it is usually possible to satisfactorily describe experimental data. The problem, however, arises when one wants to correlate the fitting parameters with real physical parameters of the ejected plume.…”

“…3,6,7 Moreover, angular resolved measurements reveal that the fitting parameters have an apparent dependence on angle of the measurement. [5][6][7][8] The fitted temperature and the stream velocity thus have to be considered only as fit parameters and their correlation with the real physical characteristics of the ablated plume is not straightforward.…”

Phase transition at low fluences in laser desorption of organic solids: a molecular dynamics study

“…The complex nature of the process has, however, hindered the progress towards the complete understanding of the phenomena of laser desorption and ablation. It is also dicult to get a microscopic picture by observing the macroscopic quantities such as yields and kinetic energies.Time-of-¯ight (TOF) measurements [15,16] of desorption yields and the kinetic energies of the ablated particles from C 6 H 6 /NaCl and C 6 H 6 /Au systems give insight into the process of laser desorption/ablation [17]. An intriguing mechanistic hypothesis has been made Braun and Hess.…”

“…Time-of-¯ight (TOF) measurements [15,16] of desorption yields and the kinetic energies of the ablated particles from C 6 H 6 /NaCl and C 6 H 6 /Au systems give insight into the process of laser desorption/ablation [17]. An intriguing mechanistic hypothesis has been made Braun and Hess.…”