Unimolecular dissociations and internal conversions of methyl halide ions

Eland, J. H. D.; Frey, R.; Kuestler, A.; Schulte, H.; Brehm, B.

doi:10.1016/0020-7381(76)80116-7

Cited by 130 publications

(168 citation statements)

References 17 publications

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“…Contrary to the observations of Eland et al [7], who report an intensity of about 20% of the total ionization, the CH 2 Br + fragment represents only 3% of the total ion intensity in the 20 eV photon energy mass spectrum recorded in this work. In the 20 eV electron impact mass spectrum, Kaposi et al [8] reported 3.2% of the total ion intensity for the CH 2 Br + fragment ion.…”

Section: (A))contrasting

confidence: 99%

“…Alternatively, the same Rydberg state involved at 12.74 eV is able to autoionize to the Ã 2 A 1 ionization continuum which subsequently dissociates. By their PEPICO experiment, Eland et al [7] could not find coincidences for H-loss and electrons corresponding to the Ã 2 A 1 state. However, these authors report also "deleterious effects of CH 3 Br" on their instrument and "a full breakdown diagram was not measured for CH 3 Br".…”

Section: (A))mentioning

confidence: 91%

“…In a photoelectron-photoion coincidence (PEPICO) experiment [7], no coincidences were observed and only the CH 3 + ion kinetic energy distribution was investigated. Speculations on the CH 2 Br + ion formation were presented.…”

Section: Introductionmentioning

confidence: 99%

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About the photoionization of methyl bromide (CH3Br). Photoelectron and photoionization mass spectrometric investigation

et al. 2006

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The threshold photoelectron (TPES) and the photoionization mass spectrometric study of CH 3 Br in the 8-20 eV photon energy range is presented. The interpretation and assignments are supported by ab initio calculations. The TPES shows several new discrete features in the Jahn-Teller split ground state X 2 E( 2 A'-2 A") of CH 3 Br + . An additional continuous band starts at about 11.8 eV. These observations are both correlated with direct ionization and autoionizing transitions. This is supported by constant ion state (CIS) spectroscopy. A large enhancement of the transitions to the A 2 A and B E states is ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak bands in the 17.5-22.0 eV photon energy range were mainly assigned to 2a 1 -1 ionization and to double excitations described essentially by the 2e -2 4a 1 1 and le -1 2e -1 4a 1 1 configurations. The photoionization mass spectrometric study allowed us to investigate in detail the ionization and dissociation of CH 3 Br + leading to CH 2 + , CH 3 + , Br + and CH 2 Br + from threshold up to 20 eV photon energy. The experimental data are compared to ab initio dissociation energies. At the onset, the CH 3 + and CH 2 Br + fragment ion production is correlated with the ground state of CH 3 Br + and both fragment ions have to appear through dissociative autoionization from the (3a 1 1 /1e 3 )6s or 5s Rydberg state. This interpretation is supported by the photoabsorption spectrum measured recently in the same photon energy range. At higher energies, beside a likely direct (pre)dissociation of the Ã 2 A 1 and B 2 E states of CH 3 Br + , autoionization also contributes to the fragmentation in all decay channels. Avoided crossings in a manifold of 2 A' states are likely to be involved. This is supported by ab initio calculations. For CH 3 + the photoion-pair process is analyzed and detailed assignments are proposed on the basis of our latest VUV photoabsorption spectroscopic data.

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Section: (A))contrasting

confidence: 99%

Section: (A))mentioning

confidence: 91%

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About the photoionization of methyl bromide (CH3Br). Photoelectron and photoionization mass spectrometric investigation

et al. 2006

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“…The ground ( 2 E 3/2 ) and first excited ( 2 E 1/2 ) states of CH 3 X + correlate with CH 3 + + X products. In the case of CH 3 Br + , the next lowest lying dissociation limit involves CH 3 + + Br* products, whereas for CH 3 I + , the larger spin-orbit splitting in atomic iodine relative to atomic bromine results in the CH 3 + I + limit lying below that for forming CH 3 + + I* products 19,23,24 . Previous photoexcitation studies involving ethyl halide cations, 5 C 2 H 5 X + , have identified the analogous CX bond fission channels and several additional pathways, each of which results in one singly charged species and one or more neutral fragments.…”

Section: Introductionmentioning

confidence: 98%

“…Starting with the first demonstration of ion 35 imaging by Chandler and Houston in 1987, 8 methyl iodide has also proven to be a popular molecule for demonstrating new experimental imaging methods in chemical dynamics, and has been widely studied by velocity-map imaging (VMI) and related techniques. [10][11][12][13] Unsurprisingly, interest has extended to the 40 photodynamics of other methyl halides (CH 3 X), and there have been several studies on CH 3 Cl, CH 3 Br, and CH 3 I in both their neutral (see 16 and references therein) and cationic forms [17][18][19][20][21][22][23][24] ; these earlier studies provide a valuable point of reference for the present investigations into the photofragmentation of two ethyl 45 halide cations, CH 3 CH 2 Br + and CH 3 CH 2 I + .…”

Section: Introductionmentioning

confidence: 99%

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Gardiner

Karsili

Lipciuc

et al. 2014

Phys. Chem. Chem. Phys.

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The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C 2 H 5 Br + and C 2 H 5 I + ) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-offlight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin-orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin-orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the R C-Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C 2 H 5 Br + cations undergo prompt C-Br bond fission to form predominantly C 2 H 5 + + Br* products with a near-limiting 'parallel' recoil velocity distribution. The observed C 2 H 3 + + H 2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C 2 H 5 + products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C 2 H 5 I + , along with an additional energetically accessible C-I bond fission channel to form C 2 H 5 + I + products. HX (X = Br, I) elimination from the highly internally excited C 2 H 5 X + cation is deemed the most probable route to forming the C 2 H 4 + fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C-C bond fission process to form CH 2 X + + CH 3 products.dissociation limit involves CH 3 + + Br* products, whereas for CH 3 I + , the larger spin-orbit splitting in atomic iodine relative

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The Dissociation Dynamics of Energy‐Selected Ions

Baer¹

1986

Advances in Chemical Physics

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Unimolecular dissociations and internal conversions of methyl halide ions

Cited by 130 publications

References 17 publications

About the photoionization of methyl bromide (CH3Br). Photoelectron and photoionization mass spectrometric investigation

About the photoionization of methyl bromide (CH3Br). Photoelectron and photoionization mass spectrometric investigation

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

The Dissociation Dynamics of Energy‐Selected Ions

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