Accurate Modeling of Infrared Multiple Photon Dissociation Spectra: The Dynamical Role of Anharmonicities

Parneix, P.; Basire, M.; Calvo, F.

doi:10.1021/jp402459f

Cited by 51 publications

(77 citation statements)

References 26 publications

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“…The discrepancy between observed and calculated spectra can be attributed to a broadening of the bands as a result of the multiple-photon excitation process in the experiment (Oomens et al 2006). As the molecule becomes energized during the excitation process, absorption bands at frequencies slightly higher than the laser frequency shift into resonance as a consequence of anharmonicity (Parneix et al 2013). This effect is more pronounced in the CH stretching range because of the high density of vibrational bands and the relatively large anharmonicities (Barker et al 1987).…”

Section: Naphthyl Anionmentioning

confidence: 92%

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons

Gao

Berden

2014

ApJ

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Based largely on infrared spectroscopic evidence, polycyclic aromatic hydrocarbon (PAH) molecules are now widely accepted to occur abundantly in the interstellar medium. Laboratory infrared spectra have been obtained for a large variety of neutral and cationic PAHs, but data for anionic PAHs are scarce. Nonetheless, in regions with relatively high electron densities and low UV photon fluxes, PAHs have been suggested to occur predominantly as negatively charged ions (anions), having substantial influence on cloud chemistry. While some matrix spectra have been reported for radical anion PAHs, no data is available for even-electron anions, which are more stable against electron detachment. Here we present the first laboratory infrared spectra of deprotonated PAHs ( [PAH -H] − ) in the wavelength ranges between 6 and 16 μm and around 3 μm. Wavelength-dependent infrared multiple-photon electron detachment is employed to obtain spectra for deprotonated naphthalene, anthracene, and pyrene in the gas phase. Spectra are compared with theoretical spectra computed at the density functional theory level. We show that the relative band intensities in different ranges of the IR spectrum deviate significantly from those of neutral and positively charged PAHs, and moreover from those of radical anion PAHs. These relative band intensities are, however, well reproduced by theory. An analysis of the frontier molecular orbitals of the even-and odd-electron anions reveals a high degree of charge localization in the deprotonated systems, qualitatively explaining the observed differences and suggesting unusually high electric dipole moments for this class of PAH molecules.

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Section: Naphthyl Anionmentioning

confidence: 92%

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons

Gao

Berden

2014

ApJ

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“…Diffraction methods [46,47] 18. Matrix isolation/vibrational circular dichroism [11,48] of sequential IR photons, dynamic energy flow within the IRMPD process is an important consideration [50]. Figure 1 provides a schematic representation of the IRMPD process.…”

Section: Infrared Multiple Photon Dissociation (Irmpd)mentioning

confidence: 99%

Determining the properties of gas-phase clusters

Hopkins

2015

Molecular Physics

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As our understanding of clusters has improved, we have found that rather than being models for surface and condensed phase phenomena, clusters often display chemical and physical properties that are quite distinct from those of their atomic constituents or associated bulk materials. Indeed, identifying and utilising the unique properties of dimensionally confined species is a major theme in nanotechnology. Consequently, numerous experimental and computational methods have been employed to investigate the structures and properties of cluster systems. In this article, the techniques of infrared multiple photon dissociation and differential mobility spectrometry are discussed using the examples of [Ag·B 12 F 12 ] − and tetraalkylammonium/solvent ionic clusters, respectively.

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“…We follow here a kinetic Monte Carlo (kMC) approach that treats those processes based on an quadratic expansion in energy levels, also known as Dunham expansion. The method has been explained in details in a recent publication, 35 so only its main features are given here. Briefly, the vibrational level structure is expanded at second order within perturbation theory, 20 EðNÞ…”

Section: Modelingmentioning

confidence: 99%

Nonlinear effects in infrared action spectroscopy of silicon and vanadium oxide clusters: experiment and kinetic modeling

Calvo

Kiawi

et al. 2015

Phys. Chem. Chem. Phys.

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For structural assignment of gas phase compounds, infrared action spectra are usually compared to computed linear absorption spectra. However, action spectroscopy is highly nonlinear owing to the necessary transfer of the excitation energy and its subsequent redistribution leading to statistical ionization or dissociation. Here, we examine by joint experiment and dedicated modeling how such nonlinear effects affect the spectroscopic features in the case of selected inorganic clusters. Vibrational spectra of neutral silicon clusters are recorded by tunable IR-UV two-color ionization while IR spectra for cationic vanadium oxide clusters are obtained by IR multiphoton absorption followed by dissociation of the bare cluster or of its complex with Xe. Our kinetic modeling accounts for vibrational anharmonicities, for the laser interaction through photon absorption and stimulated emission rates, as well as for the relevant ionization or dissociation rates, all based on input parameters from quantum on the average number of photons absorbed, which is otherwise unaccessible information: several to several tens of photons need to be absorbed to observe a band through dissociation, while three to five photons can be sufficient for detection of a band via IR-UV ionization.

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Accurate Modeling of Infrared Multiple Photon Dissociation Spectra: The Dynamical Role of Anharmonicities

Cited by 51 publications

References 26 publications

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons

Determining the properties of gas-phase clusters

Nonlinear effects in infrared action spectroscopy of silicon and vanadium oxide clusters: experiment and kinetic modeling

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