Molecular Multiphoton Spectroscopy with Ionization Detection

Johnson, Philip M.; Otis, C. E.

doi:10.1146/annurev.pc.32.100181.001035

Cited by 196 publications

(53 citation statements)

References 45 publications

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“…This would indicate that at high photon fluxes, the neutrals are either absorbing three photons causing fragmenta- tion, or ions formed previously are absorbing a photon to induce fragmentation. The relationship between the signal intensity and UV energy is similar to that observed by Zenobi's group [32] and is consistent with the theoretical treatment by Johnson and Otis [47]. Briefly, the results can be explained if one considers the processes involved in resonance enhanced two-photon ionization.…”

Section: Standard Sample Characterizationsupporting

confidence: 89%

Direct determination of polycyclic aromatic hydrocarbons in solid matrices using laser desorption/laser photoionization ion trap mass spectrometry

Specht

Blades

2003

J. Am. Soc. Mass Spectrom.

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The development and characterization of a new instrument for solid sampling which couples IR laser desorption followed by UV laser photo-ionization and analysis using an ion trap mass spectrometer has been investigated. For calibration, a new type of solid sample preparation involving activated charcoal as the solid substrate was used. This solid sample provided a steady signal for several thousand laser shots, which allowed optimization of the experimental procedure. It was found that both the IR and UV intensity and the delay between them play an important role in both the magnitude and type of signals observed. A method of gas phase accumulation with multiple laser shots was examined. Finally, this technique was demonstrated to be effective in providing direct qualitative information for N.I.S.T. SRM 1944 river sediment sample with no sample pre-treatment.

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Section: Standard Sample Characterizationsupporting

confidence: 89%

Direct determination of polycyclic aromatic hydrocarbons in solid matrices using laser desorption/laser photoionization ion trap mass spectrometry

Specht

Blades

2003

J. Am. Soc. Mass Spectrom.

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“…Therefore in terms of kinetics, if not in cross section, high I Rydberg states should show an enhanced appearance in multiphoton ionization spectra using nanosecond lasers. 9 The vibrational structure in the band whose origin appears at 60 800 cm -I correlates well with that of other Rydberg states presented here and the vibrational frequencies match those of the benzene cation rather closely. The linewidths of the observed resonances, as measured in the two photon spectrum, however, are broader than those of other Rydberg transitions in the same energy region.…”

Section: Other Rydberg Seriessupporting

confidence: 81%

“…However, saturation of the ionization step is unnecessary as long as rotational coherence is lost in the intermediate state or the transition dipole direction of the ionizing step is effectively random because of the high density of continuum states available upon ionization. 9 It has also been shown that polarization ratios greater than ideal can be obtained under the conditions of intense electric fields. 1O The thermally uncongested, collision-free conditions of the supersonic beam makes it an experimentally attractive environment for measuring polarization ratios.…”

Section: Polarization Measurementsmentioning

confidence: 99%

Higher excited states of benzene: Symmetry assignments of six gerade Rydberg series by four-photon absorption spectroscopy

Grubb

Otis

Whetten

et al. 1985

The Journal of Chemical Physics

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We report the observation of six gerade Rydberg series in benzene converging to the first ionization potential, seen in the region from 14 500–18 500 cm−1 as four-photon resonances in the five-photon ionization spectrum of the jet-cooled molecule. Polarization ratios measured for each transition in two- as well as four-photon resonance aid in determining excited state symmetries. We assign a Rydberg series with a quantum defect of 0.76 to higher members of the 3s Rydberg state first seen by Johnson in the near UV two-photon resonant three-photon ionization spectrum of benzene. The observed quantum defect, polarization ratios, and correlation with synchrotron absorption data all strongly support this assignment. Another series, with a quantum defect of 0.24, exhibits a polarization ratio of 4.5±0.5 signifying pure rank four activity. This is the first report of a purely rank four transition in a molecule. We assign this as an excitation to a d2 orbital which when converging to the first ionization potential (the 2E1g cation) gives rise to B1g and B2g Rydberg transitions. Within the D6h point group, these symmetries are allowed only in a four-photon transition. The number of gerade Rydberg series observed as four-photon resonances exceeds those available from the s-(1) and d-(3) bound members of a hydrogenic basis set. The participation of g(l=4) orbitals is indicated as the lowest members of two of the Rydberg series are at the n=5 level.

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“…This implies the possibility to restrict ion formation to occur only within this confined volume by properly adjusting the light intensity. For the present optical system, the Rayleigh length is calculated to be about 40 m with a beam waist of 2 m within this region, based on the assumption of far field conditions for a Gaussian laser beam profile [37,38]. However, since it is notoriously difficult to calculate the properties of an excimer laser beam (none of the above assumptions are valid) we have experimentally determined these critical beam parameters.…”

Section: The Dia Data Evaluationmentioning

confidence: 99%

The distribution of ion acceptance in atmospheric pressure ion sources: Spatially resolved APLI measurements

Lorenz

Schiewek

Brockmann

et al. 2008

J. Am. Soc. Mass Spectrom.

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It is demonstrated that spatially resolved mass selected analysis using atmospheric pressure laser ionization mass spectrometry (APLI MS) represents a new powerful tool for mechanistic studies of ion-molecule chemistry occurring within atmospheric pressure (AP) ion sources as well as for evaluation and optimization of ion source performance. A focused low-energy UV laser beam is positioned computer controlled orthogonally on a two-dimensional grid in the ion source enclosure. Resonance enhanced multiphoton ionization (REMPI) of selected analytes occurs only within the confined volume of the laser beam. Depending on the experimental conditions and the reactivity of the primary photo-generated ions, specific signal patterns become visible after data treatment, as visualized in, e.g., contour or pseudo-color plots. The resulting spatial dependence of sensitivity is defined in this context as the distribution of ion acceptance (DIA) of the source/analyzer combination. This approach provides a much more detailed analysis of the diverse processes occurring in AP ion sources compared with conventional bulk signal response measurements. (J

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Molecular Multiphoton Spectroscopy with Ionization Detection

Cited by 196 publications

References 45 publications

Direct determination of polycyclic aromatic hydrocarbons in solid matrices using laser desorption/laser photoionization ion trap mass spectrometry

Direct determination of polycyclic aromatic hydrocarbons in solid matrices using laser desorption/laser photoionization ion trap mass spectrometry

Higher excited states of benzene: Symmetry assignments of six gerade Rydberg series by four-photon absorption spectroscopy

The distribution of ion acceptance in atmospheric pressure ion sources: Spatially resolved APLI measurements

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