Photodissociation of o-xylene at 266 nm: imaging the CH3 dissociation channel

Time of flight (TOF) mass spectrometry is used in conjunction with a variable repelling voltage technique to elucidate the mechanism by which phenol ionizes and dissociates under 266 nm pulsed laser irradiation in combination with a 532 nm or 355 nm pulsed laser. The results suggest that, like benzene, the molecular ion is the predominant precursor of all ionic species generated in the process. Predominance of C5Hx+ species at relatively low powers confirms the presence of a low energy dissociation channel involving the elimination of CO. The use of a second laser at 532 nm is found to selectively destroy the C5Hx+ (as compared to the parent ion) species. The parent ion is found to be protected from the radiation of the second laser pulse at 532 nm but not at 355 nm if the second laser pulse is delayed by 50 ns. This is explained in terms of relaxation within the parent ion energy levels, the location of a low energy dissociation channel and the wavelengths of the lasers used. The main aspects of the fragmentation pattern are discussed in terms of the statistical theory of Rebentrost and Ben-Shaul.

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A theoretical study of the structures and stabilities of C2H3S+ ions

Canadian Journal of Chemistry ◽

10.1139/v87-203 ◽

1987 ◽

Vol 65 (6) ◽

pp. 1209-1213 ◽

Cited By ~ 7

Author(s):

Christopher F. Rodriquez ◽

Alan C. Hopkinson

Keyword(s):

Experimental Observation ◽

Molecular Orbital ◽

Global Minimum ◽

Theoretical Study ◽

Saddle Points ◽

Intramolecular Rearrangement ◽

Molecular Orbital Calculations ◽

Dissociation Channel ◽

Transition Structures

Abinitio molecular orbital calculations at the 6-31G* level have been used to locate eight minima and five saddle points on the C2H3S+ hypersurface. The thioacetyl ion, H3CCS+ (1), is the global minimum and the 1-thiovinyl cation (4), 106 kJ mol−1 higher, is the next lowest. Interconversion of 1 and 4 has the highest barrier calculated for this surface (250 kJ mol−1 above 4) but all transition structures to intramolecular rearrangement are lower than the energies of the dissociation products. These results are consistent with the experimental observation that there is only one dissociation channel for ions C2H3S+, regardless of the structure of organosulphur compound from which C2H3S+ was produced. Comparisons are made with the C2H3O+ hypersurface.

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General discussion: electronic emission spectroscopy of CF+4 and SiF+4

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1988.0018 ◽

1988 ◽

Vol 324 (1578) ◽

pp. 289-293 ◽

Cited By ~ 3

Keyword(s):

Emission Spectroscopy ◽

Molecular Beam ◽

Rotational Temperature ◽

Electronic States ◽

Emission Spectra ◽

Fluorescence Decay ◽

Molecular Ions ◽

Dissociation Channel ◽

Excited Electronic States ◽

Beam Electron

We report the observation of electronic emission spectra in the tetrahedral molecular ions CF+4 and SiF+4. The spectra are observed at a low rotational temperature (less than 30 K) in a crossed molecular-beam - electron-beam apparatus (Carrington & Tuckett 1980). These spectra are especially interesting because the fluorescing states in the two ions lie up to 10 eV above their lowest dissociation channel (to CF+3/SiF+3 + F; see figure 1), and these states might be expected to decay non-radiatively rather than by a radiative channel. The observation of fluorescence decay from highly excited electronic states of these polyatomic ions is therefore a very surprising phenomenon.

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