Photofragment ions

Fig. 17. Photofragment ion images of C6H5CD3 in three different mass regions. Image of m/e = 76 in (b) resulted from two-photon dissociation. Image of parent molecule m/e = 95, and m/e = 96, 97 due to the 13C natural abundance are shown in (c).

The Mg+ complexes of cytosine, thymine and uracil are the most complex system studied via photodissociation spectroscopy to date . A complication for these systems is that these nucleobases can exist in various tautomeric forms and that complexation of a metal can change the stability order of the tautomers. DFT calculations located four tautomeric Mg(cytosine)+ complexes, and three of these (29, 30, and 31) were suggested to be responsible for the four reactive photofragment ions 32-35 observed at a wavelength of 360 nm (Scheme 4) . Related photofragmentation reactions were observed for the Mg(thymine)+" and Mg(uracil)+" complexes . ... 

An ion of nominal m/z 442 was produced from cis-dichloro-trans-dihydroxo-bis-2-propanamine/platinum (IV) (CHIP) by ion/molecule reactions (IMR) of the major electron impact (El) fragment ion with the neutral molecule. As shown in Figure 3, this ion dissociated when irradiated by the cw laser for ca. 500 ms to produce two daughter photofragment ions, m/z 366 and m/z 311, by loss of various ligands (Equation 1). 

Fig. 7. TOF tandem mass spectrometer. The mass gate selects the ions of interest for photoexcitation by the tunable pulse infrared laser. Photofragment ions are mass-resolved by the reflectron mass spectrometer. (Jude Kelley and Mark A. Johnson, private communication.)...

Cooper et al. [98Coo] and Jee et al. [98Jee] have carried out photofragment ion imaging studies in the excitation range between 260 and 580 mn. 

Photochemistry of gas-phase molecules, including species of atmospheric importance the molecular photodissociation dynamics are traced by photofragment ion (velocity map) imaging. 

Parker D, Eppink A. (1997) Velocity map imaging of ions and electrons using electrostatic lenses Apphcation in photoelectron and photofragment ion imaging of molecular oxygen. Rev. Sci. Instr. 68 3477-3484. 

A high-intensity source of photons is required to produce detectable numbers of photofragment ions from a mass-selected ion beam. For this reason, most experiments have used a laser for the photodissociation process. Continuous lasers generally produce the highest average power outputs, with an excellent stability and a very narrow photon energy bandwidth eV). They may be used to pump a dye... 

As in threshold photoionization experiments, photofragment ion concentrations are extremely low and it is necessary to utilize signal-enhancement techniques. Although phase-sensitive detection has been used, it is more usual to employ signal-averaged pulse counting. For photodissociation with a pulsed laser, an appropriate gating system synchronized... 

Photofragment ion imaging is now an established method for the measurement of photofragment velocity (speed and angle) distributions from unimolecular dissociation processes. Recently, the domain of the ion imaging technique has been expanded to investigate bimolecular reactions as well, with the aim of... 

Heck AJR (1997) Throwing light on molecules falling apart photofragment ion imaging. European Mass Spectrometry 3 171-183. 

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