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See detailA photoionization mass spectrometric and threshold photoelectron-photoion coincidence study of vinylbromide (C2H3Br) in the vacuum ultraviolet range of 6-21 eV.
Hoxha, A.; Yu, S.-Y.; Locht, Robert ULg et al

in Chemical Physics (2011), 379(1-3), 99-108

The dissociative photoionization of vinyl bromide (C2H3Br) has been investigated by photoionization mass spectrometry (PIMS) and time-of-flight threshold photoelectron-photoion coincidence (TOF-TPEPICO ... [more ▼]

The dissociative photoionization of vinyl bromide (C2H3Br) has been investigated by photoionization mass spectrometry (PIMS) and time-of-flight threshold photoelectron-photoion coincidence (TOF-TPEPICO) spectrometry using synchrotron radiation. The photoionization efficiency curves of the three most abundant ions, i.e. C2H3Br+, C2H3+ and C2H2+, are measured and analyzed in detail. A C2H3+/Br- photoion-pair formation process has been detected for the first time. Some arguments are provided in favor of the electronic excitation of the C2H3+ fragment and of the isomerization of the C2H2+ ions. The breakdown diagram for these ions in the 9.8–21 eV photon energy range, derived from TOF-TPEPICO mass spectra, is discussed. The involvement of the successive C2H3Br+ ionic states and the role of autoionization of C2H3Br Rydberg states are emphasized. For the two minor HBr+ and Br+ fragment ions only the breakdown diagrams are measured and appearance energies are derived. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. I. A Rydberg Series Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In the higher energy range of 12-25 eV very weak diffuse bands are mostly assigned to transitions from the 3a1, 1e and 2a1 to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness of the features is very variable over the entire spectral region. In a first step, the interpretation of the spectrum and the assignment of the Rydberg transitions is based on the simple Rydberg formula. The observed features are classified in two groups of four series, each converging to one of the two spin-orbit components of the X2E state of CH3Cl+. Rydberg series of nsa1 (delta=1.069 and 1.064), npa1 (delta= 0.68 and 0.66), npe (delta= 0.438 and 0.427) and nd (delta= -0.040 and -0.092) characters are observed. The same measurements have been made for the first time on CD3Cl in the 6-12 eV photon energy range. The same Rydberg transitions are observed. Analogous series are characterized by about the same delta values: nsa1 (delta= 1.038 and 0.968), npa1 (delta= 0.65 and 0.61), npe (delta= 0.458 and 0.462) and nd (delta= -0.004 and -0.082). Ionization energies for CD3Cl X2E3/2 at 11.320 eV and X2E1/2 at 11.346 eV are deduced. In a second step, we fitted the experimental data for the nsa1 and npa1 states to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. This accounts for the progressive switching from Hund's case (a) to Hund's case (c). [less ▲]

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See detailAbout the Photoionization of Methyl Chloride. A Threshold Photoelectron Spectroscopic and Photoionization Mass Spectrometric investigation.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and ... [more ▼]

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and assignments are supported by ab initio calculations. The detailed analysis of the TPES shows numerous features in the Jahn-Teller split ground X2E(2A'-2A") state of CH3Cl+ and a new continuus band peaking at 13.4 eV. These were assigned to both direct ionization and autoionizing transitions. The transitions to the A2A1 and to the B2E states undergo a large enhancement ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak signals in the 19-26 eV photon energy range were mainly assigned to 2a1-1 ionization and to double excitations described essentially by 2e-2, 4a11 and 1e-1, 2e-1, 4a11 configurations. The PIMS study allowed us to investigate in detail the ionization and dissociation of CH3Cl+ into CH2+, CH3+, CHCl+ and CH2Cl+ from threshold up to 20 eV photon energy. At the onset, the CH3+, CHCl+ and CH2Cl+ fragment ion production is correlated to the ground state of CH3Cl+ and all fragment ions have to appear through dissociative autoionization from the 2e->3p Rydberg state. This interpretation is supported by the photoabsorption spectrum (PAS) measured recently in the same photon energy range. At higher energies, beside direct dissociation of the A2A1 and B2E states of CH3Cl+ autoionization also contributes to the fragmentation in all decay channels. For CH3+ the photoion-pair process is analyzed and detailed assignments are proposed on the basis of recent PAS data. [less ▲]

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See detailThe Vacuum UV Photoabsorption spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. II. A vibrational Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and ... [more ▼]

The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and assigned to vibrational excitation accompanying a series of Rydberg transitions. The vibronic transitions involve both Jahn-Teller distortion and spin-orbit splitting. The former effect has been evaluated by ab initio calculations showing that the 2E state (in the C3v symmetry group) splits into 2A' and 2A" states in the Cs symmetry group. The 2A' state is energetically the lowest component whereas the 2A" is found to be a transition state. The Jahn-Teller stabilisation energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described by using the vibrational modes, i.e. hcomega5= 104+/-7 meV, hcomega6= 77+/-7 meV and homega=162+/-3 meV respectively, as resulting from an average over all the analyzed Rydberg states. In CD3Cl the corresponding energies are hcomega5= 81+/-4 meV, hcomega6= 66+/-5 meV and hcomega= 124+/-4 meV. These values are in good agreement with those predicted by the present ab initio calculations for the ion ground state. However, the agreement is not so good for the wavenumber omega which could be assigned to the nu3 or nu4 vibrational modes. Though some arguments favour nu4 (the CH3 umbrella mode), within the error limits on the present measurements it is formally not possible to ascribe this wavenumber to one of these two vibrations. [less ▲]

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See detailUnimolecular Reaction Dynamics from Kinetic Energy Release Distributions: extent of Phase Space Sampling.
Hoxha, A.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Gelpi, Ed. (Ed.) 15th International Mass Spectrometry Conference: Book of Abstracts. (2000)

The dissociative photoionization of C2H3Br+ in the Br and HBr loss channels is reported. The KER distributions are analyzed by the Maximum Entropy Method (MEM). It can be concluded that at low and high ... [more ▼]

The dissociative photoionization of C2H3Br+ in the Br and HBr loss channels is reported. The KER distributions are analyzed by the Maximum Entropy Method (MEM). It can be concluded that at low and high internal energy the dissociations are statistical. At intermediate internal energies the excess energy is not completely randomized. [less ▲]

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See detailThe photoabsorption and Constant Ion State Spectroscopy of Vinyl Bromide.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Chemical Physics (2000), 260

In this paper we report the photoabsorption and the constant ion state spectroscopy of vinyl bromide (C2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in ... [more ▼]

In this paper we report the photoabsorption and the constant ion state spectroscopy of vinyl bromide (C2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in detail between 5.0 and 12.0 eV photon energy revealing many previously unobserved structures. These features were analyzed in terms of valence to virtual valence transitions and Rydberg series. The examination of the three Rydberg series converging towards the first ionization threshold (2a"->ns, 2a"->np and 2a"->nd) leads to wavenumbers of 335+/-30, 690+/-30 and 1305+/-30 cm-1. The vibrational wavenumbers of the progressions belonging to Rydberg series converging towards the second ionization threshold are 485+/-30 and 1145+/-50 cm-1. Ab initio calculations helped the assignment of the valence transitions and of the observed vibrational wave numbers in the Rydberg series. Constant Ionic State spectra were recorded for vibronic states corresponding to the first and the second electronic states of the ion. Their fine structures are assigned to the autoionization of Rydberg states. The autoionization decay of these Rydberg states is analyzed qualitatively in terms of the vibrational nature of the final ionic state. [less ▲]

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See detailAbout the Vacuum UV Photoabsorption Spectrum of Methyl Fluoride (CH3F): the fine structure and its vibrational analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2000), 257

The vacuum UV photoabsorption spectrum of CH3F has been recorded between 7 and 24 eV and has been analyzed in detail. Broad and structureless peaks are observed over the entire photon energy range. They ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3F has been recorded between 7 and 24 eV and has been analyzed in detail. Broad and structureless peaks are observed over the entire photon energy range. They are all assigned to transitions to Rydberg states, members of series converging to the 2e-1, 5a-1 and 1e-1 ionization limits. These features are underlying very long series of narrow and weak structures in the range of 10-13.2 eV. Through a continuum subtraction procedure, about 70 lines could clearly be identified. These have been assigned to long vibrational progressions belonging to Rydberg states corresponding to the 2e->3p and 2e->6s/5d configurations. These states are split by a Jahn-Teller distortion. Ab initio calculations lead to a Jahn-Teller stabilization energy of about 0.84 eV. The main features observed in the two bands are assigned to one single long vibrational progression of hcomega=0.160 eV (1290cm-1) related to the C-F Jahn-Teller inactive stretching vibration. The remaining structure is assigned to the low excitation of the Jahn-Teller active vibrational modes, i.e. the bending modes nu5 and nu6 characterized by hcomega5=0.120 eV (970 cm-1) and hcomega6=0.082 eV (660 cm-1). Leaning on the present results and assignments previously reported photoelectron spectroscopic data on CH3F+ [L. Karlsson, R. Jadrny, L. Mattsson, F.T. Chau, K. Siegbahn Phys.Scripta 16 (1977) 225] have been reconsidered and reinterpreted. [less ▲]

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See detailPhotoelectron Spectroscopy of Vinyl Bromide and Intramolecular Dynamics of the ionic B state.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Chemical Physics (2000), 256

In this paper we report the He(I) photoelectron spectrum (PES) and the threshold photoelectron spectrum (TPES) of C2H3Br. The fine structure in the first two ionic states in the He(I) spectrum is assigned ... [more ▼]

In this paper we report the He(I) photoelectron spectrum (PES) and the threshold photoelectron spectrum (TPES) of C2H3Br. The fine structure in the first two ionic states in the He(I) spectrum is assigned to progressions belonging partially to previously unobserved vibrational modes. The TPES has been measured between 9.0 and 25.0 eV, and the photon energy range of 9.8-12.0 eV has been investigated in more detail. Extensive calculations with the GAUSSIAN set of programs have been performed to help in the assignment of the observed features. Furthermore, a conical intersection between the A2A" and the B2A" states was found to take place along the C-Br stretching coordinate. Intramolecular dynamics of the B2A" state, initially prepared in the Franck-Condon region, was probed by the Fourier transform of the spectrum. The B2A" state is almost readily depleted, most probably due to a very effective internal cnversion through the conical intersection. [less ▲]

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See detailUnimolecular Dynamics from Kinetic Energy Release Distributions. V. How does the Efficiency of Phase Space Sampling vary with Internal Energy?
Hoxha, A.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Journal of Chemical Physics (1999), 111(20), 9259-9266

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions (KERDs) for C2H3Br+->[C2H3]++Br dissociation as a function of the ... [more ▼]

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions (KERDs) for C2H3Br+->[C2H3]++Br dissociation as a function of the internal energy. The KERDs obtained by dissociative photoionization using the He(I), Ne(I) and Ar(II) resonance lines were analyzed by the maximum entropy method and were found to be well described by introducing a single dynamical constraint, namely the relative translational momentum of the fragments. Ab initio calculations reveal the highly fluxional character of the C2H3+ ion. As the energy increases, several vibrational modes are converted in turn into large-amplitude motions. Our main result is that, upon increasing internal energy, the fraction of phase space sampled by the pair of dissociating fragments is shown to first decrease, pass through a shallow minimum around 75%, and then increase again, reaching almost 100% at high internal energies (8 eV). This behaviour at high internal energies is interpreted as resulting from the conjugated effect of intramolecular vibrational redistribution (IVR) and radiationless transitions among potential energy surfaces. Our findings are consistent with the coincidence data of Miller and Bear, reanalyzed here, and with the KERD of the metastable dissociation. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectrum of Methyl Fluoride (CH3F). A vibrational Analysis.
Locht, Robert ULg; Hoxha, A.; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1999)

The vacuum photoabsorption spectrum of CH3F has been recorded using synchrotron radiation dispersed at medium resolution. Special data handling has been applied. The vibrational structure of about 70 ... [more ▼]

The vacuum photoabsorption spectrum of CH3F has been recorded using synchrotron radiation dispersed at medium resolution. Special data handling has been applied. The vibrational structure of about 70 features has been analyzed for the first time. [less ▲]

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See detailThe Photoionization of Vinyl Bromide Clusters.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Sthrahlung m.b.H (1999)

The optimization of the conditions for cluster production from C2H3Br is investigated. The dissociative photoionization of these species is reported, e.g. [C2H2Br]2+->C4H6Br++Br. An intracluster Penning ... [more ▼]

The optimization of the conditions for cluster production from C2H3Br is investigated. The dissociative photoionization of these species is reported, e.g. [C2H2Br]2+->C4H6Br++Br. An intracluster Penning ionization phenomenon is observed. [less ▲]

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See detailThree-dimensional Kinetic Energy Distributions of Ions using a Retarding Potential Analyser. Analysis of Discimination Effects by Ion Trajectory Simulations.
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg

in Rapid Communications in Mass Spectrometry : RCM (1999), 13

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were ... [more ▼]

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were performed which led to an analytical function correcting for the influence of discrimination against ions with velocity components perpendicular to the retarding field direction. The analysis of the thermal kinetic energy distribution of molecular vinyl bromide ions confirms the computed correcting factor. [less ▲]

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See detailReactivity of Halogenoethylene Ions using Photoionization and Collisional Activation.
Leyh, Bernard ULg; Hoxha, A.; Franck, B. et al

in Karjalainen, E. J.; Hesso, A. E.; Jalonen, J. E. (Eds.) et al Advances in Mass Spectrometry: Volume 14. (1998)

Unimolecular reactivity of ionized difluoroethylene and vinylbromide have been investigated using photoionization mass spectrometry and tandem mass spectrometry. Kinetic energy release distributions ... [more ▼]

Unimolecular reactivity of ionized difluoroethylene and vinylbromide have been investigated using photoionization mass spectrometry and tandem mass spectrometry. Kinetic energy release distributions corresponding to HF- and F- losses from 1,1-C2H2F2+ and to Br-loss from C2H3Br+ have been determined. At low internal energy the loss of HF from C2H2F2+ leads to the fluoroacetylene cation with a large kinetic energy release (0.4-2.5 eV) while at higher energy a new channel is opened, leading to C=CHF+ (fluorovinylidene) with a much smaller kinetic energy release (0.0-0.2 eV). For the F-loss from C2H2F2+ and the Br-loss from C2H3Br+ bimodal distributions have been observed. The possible role of excited states in these dissociations is discussed. [less ▲]

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See detailThe Photoionization of small Vinyl Bromide (C2H3Br)n Clusters.
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1998)

The ionization and decomposition of small clusters produced from C2H3Br are investigated by threshold photoelectron-photoion coincidence spectroscopy.

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See detailThe threshold Photoelectron-Photoion Coincidence Spectroscopy of Vinyl Bromide (C2H3Br).
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1998)

The dissociative ionization of C2H3Br has been investigated by threshold photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The C2H3+, C2H2+, HBr+ and Br+ dissociation channels ... [more ▼]

The dissociative ionization of C2H3Br has been investigated by threshold photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The C2H3+, C2H2+, HBr+ and Br+ dissociation channels were considered. [less ▲]

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See detailThe Photoionization of Methyl Iodide (CH3I). The Threshold Photoelectron and CIS Spectroscopy.
Locht, Robert ULg; Hoxha, A.; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1997)

The vacuum UV photoabsorption spectrum of CH3I and its threshold photoelectron spectrum are reported. The region of 9.5-10.5 eV photon energy is recorded at high resolution.

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See detailThe Photoionization of Ethylene Monobromide (C2H3Br). The Threshold Photoelectron and CIS Spectroscopy.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Elektronen Synchrotron Strahlung m.b.H (1997)

The first results on the threshold photoelectron, CIS-spectroscopy and photoabsorption spectroscopy of C2H3Br are reported. A first analysis is presented.

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See detailReaction Dynamics of Collisionally activated Ammonia Cations.
Leyh, Bernard ULg; Hoxha, A.

in Chemical Physics (1994), 179

In the framework of a research on the collisional mechanisms involved in tandem mass spectrometry, the collisional activation processes of NH3+ with different target gases have been investigated. The ... [more ▼]

In the framework of a research on the collisional mechanisms involved in tandem mass spectrometry, the collisional activation processes of NH3+ with different target gases have been investigated. The experiments have been performed on an upgraded AEI-MS9 sector instrument equipped with two collision cells and include daughter ion spectra, ion kinetic energy spectra, determination of kinetic energy release distributions (KERD) and appearance energy measurements. We have shown that collisionally activated dissociation (CAD) of NH3+ into NH++[H,H] depends upon the internal energy of NH3+. This internal energy effect is also observed for the NH2++H channel, when Xe is the target gas; with He, such an effect could not be detected. The analysis of the KERD shows that production of NH2+ upon CAD takes place from the NH3+ ground electronic state by rotational predissociation; two components are observed, one which corresponds to a near-threshold process (mean kinetic energy release <T>=0.13 eV), and one characterized by <T>=0.56 ev corresponding to an excess energy of 2.1 eV above the dissociation threshold. NH+ fragments can be formed by two processes: the first one occurs at threshold and leads to NH+(X2Pi)+H2(X1Sigma+g); the second one is characterized by large KER values (up to 7 eV) and leads to either electronically excited NH+ or dissociation of H2. [less ▲]

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