Photofragment

Rosker M J, Rose T S and Zewail A 1988 Femtosecond real-time dynamics of photofragment-trapping resonances on dissociative potential-energy surfaces Ghem. Phys. Lett. 146 175-9... 

Figure A3.5.L The fast ion beam photofragment spectrometer at SRI International. L labels electrostatic lenses, D labels deflectors and A labels apertures.

Figure A3.5.2. The Ar photofragment energy spectmm for the dissociation of fiions at 752.5 mn. The upper scale gives the kinetic energy release in the centre-of-mass reference frame, both parallel and antiparallel to the ion beam velocity vector in the laboratory.

Moseley J and Durup J 1981 Fast ion beam photofragment spectroscopy Annual Review of Physical Chemistry ed B S Rabinovitch, J M Schurr and H L Strauss (Palo Alto, CA Annual Reviews)... 

Moseley J T 1985 Ion photofragment spectroscopy Photodissociation and Photoionization ed K P Lawley (New York Wiley)... 

Ashfold M N R, Mordaunt D H and WIson S H S 1996 Photodissociation dynamics of hydride molecules H atom photofragment translational spectroscopy Adv. Photochem. 21 217-95... 

Boyarkine O V, Settle RDF and Rizzo T R 1995 Vibrational overtone spectra of jet-cooled CFgH by infrared laser assisted photofragment spectroscopy Ber. Bunsenges. Rhys. Chem. 99 504-13... 

Pugiiano N, Szarka A Z, Gnanakaran S, Trieohei M and Hoohstrasser R M 1995 Vibrationai popuiation dynamios of the Hgi photofragment in ethanoi soiution J. Chem. Phys. 103 6498-511... 

Many readers will have some familiarity with the standard expressions for the angular distribution of photofragments ejected from a randomly oriented (gas-phase) molecule by perfectly polarized light ... 

We use laser photofragment spectroscopy to study the vibrational and electronic spectroscopy of ions. Our photofragment spectrometer is shown schematically in Eig. 2. Ions are formed by laser ablation of a metal rod, followed by ion molecule reactions, cool in a supersonic expansion and are accelerated into a dual TOE mass spectrometer. When they reach the reflectron, the mass-selected ions of interest are irradiated using one or more lasers operating in the infrared (IR), visible, or UV. Ions that absorb light can photodissociate, producing fragment ions that are mass analyzed and detected. Each of these steps will be discussed in more detail below, with particular emphasis on the ions of interest. 

Photofragment spectroscopy is extremely sensitive, but it has the disadvantage that one is only sensitive to absorption that leads to photodissociation. For single-photon experiments, this means that one is restricted... 

Methane-to-methanol conversion by gas-phase transition metal oxide cations has been extensively studied by experiment and theory see reviews by Schroder, Schwarz, and co-workers [18, 23, 134, 135] and by Metz [25, 136]. We have used photofragment spectroscopy to study the electronic spectroscopy of FeO" " [47, 137], NiO [25], and PtO [68], as well as the electronic and vibrational spectroscopy of intermediates of the FeO - - CH4 reaction. [45, 136] We have also used photoionization of FeO to characterize low lying, low spin electronic states of FeO [39]. Our results on the iron-containing molecules are presented in this section. 

Figure 12. Vibrational action spectra of V (OCO) in the OCO antisymmetric stretch region, (a) Spectrum obtained by monitoring depletion in the photofragment produced by irradiation at the vibronic origin at 15,801 cm The IR absorption near 2391.5 cm removes molecules from V[" = 0, leading to an 8% reduction in the fragment yield, (b) Spectrum obtained by monitoring enhancement in the VO+ photofragment signal as the IR laser is tuned, with the visible laser fixed at 15,777 cm (the Vj = 1 v" = 1 transition). The simulated spectrum gives a more precise value of the OCO antisymmetric stretch vibration in V" (OCO) of 2392.0 cm .

Fig. 8. Photofragment center-of-mass translational energy distribution P(Et) and anisotropy distribution 0 Et) for the photolysis of C2H2. The arrows mark the energetic thresholds for the corresponding electronic states of the fragment C2H. The out-of-phase correlation between the mild oscillations of 0 and the structures in P(Et) is indicated by vertical dashed lines.

Fig. 11. Photofragment translational energy distribution (upper panel) and anisotropy distribution (lower panel) for the photolysis of H2S. The arrow in the upper panel marks the energetic onset for the generation of SH(A2S+, 1/) + H.

J. Helpburn, Photofragment translational spectroscopy, Atomic and Molecular Beam Methods, ed. G. Scoles (Cambridge Press). 

In addition to the previously mentioned disadvantages, all of these methods have another drawback in the large molecule photofragment velocity measurements. For example, in the studies of UV photon photodissociation of polyatomic molecules, like alkene and aromatic molecules, molecules excited by the UV photons quickly become highly vibrationally excited in the ground electronic state through fast internal conversion, and dissociation occurs in the ground electronic state. 

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).

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