Ion-pair formation mechanisms in chloromethane, bromomethane and dichlorodifluoromethane

Shaw, David; Holland, D.M.P.; Walker, Isobel C.

doi:10.1088/0953-4075/39/17/012

Cited by 25 publications

(46 citation statements)

References 40 publications

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“…This small value, coupled with the fact that fluorescence from SF 5 CF 3 * is unlikely to have a large quantum yield, suggests strongly that predissociation into neutral fragments is the favoured process at this energy. A similar conclusion was reached by Shaw et al [37] in a comparable study of the dissociation dynamics of Rydberg states of some substituted methane molecules. The agreement of peak positions in SF 5 CF 3 between the photoabsorption spectrum [20], the total fluorescence yield [36], and the F -ion yield extends up to 17 eV, but above this energy similarities between the spectra are less clear.…”

Section: Trifluoromethyl Sulphur Pentafluoride (Sf 5 Cf 3 )supporting

confidence: 83%

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Simpson

2011

Two Studies in Gas-Phase Ion Spectroscopy

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Section: Trifluoromethyl Sulphur Pentafluoride (Sf 5 Cf 3 )supporting

confidence: 83%

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Simpson

2011

Two Studies in Gas-Phase Ion Spectroscopy

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“…Absolute cross sections and quantum yields for production of X − , CH 2 c The AE(F − ) given here assumes that the peak at 22.5 eV in Figure 1(b)) is overlap of CHF − signal.…”

Section: Discussionmentioning

confidence: 99%

“…(2a 1 ) 2 (1e) 4 (3a 1 ) 2 (2e) 4 , where the 2e orbital is essentially non-bonding X npπ orbitals and the three lower orbitals arise from the σ-bonding framework formed from overlap of the C 2s (a 1 ), C 2p (a 1 +e) with 3H…”

Section: Ae(a − ) ≥ Ie(ab) + D O (A−b + ) − Ea(a) (Ii)mentioning

confidence: 99%

“…Given the number of corrections made to the anion signals in the two experiments, this discrepancy falls within a reasonable expected experimental uncertainty. The average value of k was then used in Equation (1) to determine the absolute cross sections, σ, in units of cm 2 , for production of X − , CH 2 X − and CHX − from CH 3 X. We estimate that these cross sections are accurate to a factor of ca.…”

mentioning

confidence: 99%

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Vacuum-UV negative photoion spectroscopy of CH3F, CH3Cl and CH3Br

Rogers

Tuckett

Dunn

et al. 2010

Phys. Chem. Chem. Phys.

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Using tunable vacuum-UV radiation from a synchrotron, negative ions are detected by quadrupolar mass spectrometry following photoexcitation of three gaseous halogenated methanes CH 3 X (X = F,Cl,Br). The In common with many quadrupoles, the spectra of m/z 1 (H − ) anions show contributions from all anions, and only for CH 3 Br is it possible to perform the necessary subtraction to obtain the true H − spectrum.The anion cross sections are normalised to vacuum-UV absorption cross sections to obtain quantum yields for their production. The appearance energies of X − and CH 2 X − are used to calculate upper limits to 298 K bond dissociation energies for D o (H 3 C−X) and D o (XH 2 C−H) which are consistent with literature values. The spectra suggest that most of the anions are formed indirectly by crossing of Rydberg states of the parent molecule onto an ion-pair continuum. The one exception is the lowestenergy peak of F − from CH 3 F at 13.4 eV, where its width and lack of structure suggest it may correspond to a direct ion-pair transition.

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“…A similar conclusion was reached by Shaw et al in a comparable study of the dissociation dynamics of Rydberg states of some substituted methane molecules. 23 The agreement of peak positions in SF 5 CF 3 between the photoabsorption spectrum, 20 the total fluorescence yield 48 and the F − ion yield extends up to 17 eV, but above this energy similarities between the spectra are less clear.…”

Section: II Yield Of Sfmentioning

confidence: 98%

Vacuum-UV negative photoion spectroscopy of SF5CF3

Simpson

Tuckett

Dunn

et al. 2008

The Journal of Chemical Physics

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___________________________________________________________________________________Ion pair formation, generically described as AB → A + + B − , from vacuum-UV photoexcitation of trifluoromethyl sulfur pentafluoride, SF 5 CF 3 , has been studied by anion mass spectrometry using synchrotron radiation in the photon energy range 10−35 eV. The anions F − , F 2 − and SF x − (x = 1−5) are observed. With the exception of SF 5 − , the anions observed show a linear dependence of signal with pressure, showing that they arise from ion pair formation. SF 5 − arises from dissociative electron attachment, following photoionization of SF 5 CF 3 as the source of low-energy electrons. Cross sections for anion production are put on to an absolute scale by calibration of the signal strengths with those of F − from both SF 6 and CF 4 .Quantum yields for anion production from SF 5 CF 3 , spanning the range 10 −7 to 10 −4 , are obtained using vacuum-UV absorption cross sections. Unlike SF 6 and CF 4 , the quantum yield for F − production from SF 5 CF 3 increases above the onset of photoionization.3

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Ion-pair formation mechanisms in chloromethane, bromomethane and dichlorodifluoromethane

Cited by 25 publications

References 40 publications

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Vacuum-UV negative photoion spectroscopy of CH3F, CH3Cl and CH3Br

Vacuum-UV negative photoion spectroscopy of SF5CF3

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