Laser Tandem Mass Research Articles

Multiphoton Dissociation of Organic Molecules: Step by Step Investigation with Laser Tandem Mass Spectrometry

AbstractMultiphoton ionization of molecules is connected with strong multiphoton dissociation of the molecular ions for high enough laser intensities. By varying the laser intensity, the degree of dissociation can be tuned from very soft (no fragmentation) to extremely hard. In earlier work we proposed and proved the “ladder‐switching” model to explain this process for excitation with nanosecond laser pulses. Recently, we developed a new laser tandem mass spectrometric technique which allows to investigate the fragmentation paths due to the “ladder‐switching” mechanism step by step. We applied this method to benzene cations and could verify the proposed tree of fragmentation pathways. Also a wavelength dependence of the fragmentation pattern has been detected and explained. Our new technique includes (i) a two stage ion source with laser ionization and second order space focus, (ii) secondary laser excitation and dissociation in this space focus and (iii) a reflectron time‐of‐flight analyzer.

Laser Tandem Mass Spectrometry in a Time of Flight Instrument

Abstract We present a new laser tandem mass spectrometry technique in a reflectron time of flight (TOF) instrument. A first pulsed laser performs the multiphoton ionization and the primary photodissociation. A newly designed ion source permits a high mass resolution in the space focus of the 12 cm long first linear TOF, where then the secondary excitation can take place. For high resolution applications the pure secondary or pure metastable mass spectrum of a preselected precursor ion can be recorded using a new reflectron scanning technique. It is also possible to obtain the whole secondary mass spectrum with one cycle using a new postacceleration method. Several techniques for ejection of interfering ions are shown. The features of our techniques are demonstrated at various primary fragments of benzene.