C. Kosmidis

Resonant ionization of oxygen and hydrogen atoms following laser-induced photodissociation of nitrobenzene vapour

The resonant ionization of oxygen and hydrogen atoms has been observed in a linear time-of-flight (TDF) mass spectrometer during studies of the resonance enhanced multiphoton ionization (REMPI) of nitrobenzene vapour in the wavelength region 225-245 nm. Oxygen ions have been observed in the mass spectrum in the region of 226 nm. and have been identified as arising from the 2p4 3 P to 2p33p 3P two-photon transition in atomic oxygen. A large enhancement in the hydrogen ion yield from nitrobenzene was also recorded when the laser wavelength was tuned through the 1s 2S to 2s 2S two-photon transition of atomic hydrogen at 243.13 nm. The large on-resonance enhancements in both signals indicate that oxygen and hydrogen atoms are produced in abundance during the interaction between ultraviolet laser light and nitrobenzene vapour.

The detection of energetic materials with a laser ionization ion mobility spectrometer

Laser induced multiphoton ionization (MPI) has been used to produce positive and negative ions at atmospheric pressure in an ion mobility spectrometer. This paper deals particularly with the application of this technique to the ultra‐trace detection of a number of energetic materials such as RDX and PETN.In conventional ion mobility spectrometry (IMS), a radioactive 63Ni β‐foil is used as the ionization source. The laser IMS spectra will be compared with the 63Ni spectra and it will be shown that the analyte ions produced by laser ionization have a wavelength dependent fingerprint which provides an additional degree of selectivity. It is felt that this new approach to IMS will develop considerably the scope and applicability of this powerful technique.Laser induced multiphoton ionization (MPI) has been used to produce positive and negative ions at atmospheric pressure in an ion mobility spectrometer. This paper deals particularly with the application of this technique to the ultra‐trace detection of a number of energetic materials such as RDX and PETN.In conventional ion mobility spectrometry (IMS), a radioactive 63Ni β‐foil is used as the ionization source. The laser IMS spectra will be compared with the 63Ni spectra and it will be shown that the analyte ions produced by laser ionization have a wavelength dependent fingerprint which provides an additional degree of selectivity. It is felt that this new approach to IMS will develop considerably the scope and applicability of this powerful technique.

Investigations of desorbed species from matrix materials used in MALDI

Despite the widespread use of Matrix Assisted Laser Desorption Ionization (MALDI), the processes involved in ion formation have yet to be satisfactorily explained. Protonation processes have been suggested as a possible method for the creation of the analyte ions. In this work, the existence of neutral hydrogen atoms in the ablation plume is investigated by using the postionization (PI) technique. Neutral atomic hydrogen is ionized through a (2+1) resonant excitation ionization scheme. The mass spectra at different delay times between the ablation and PI lasers have demonstrated the existence of hydrogen atoms with high velocities in the ablated plume.