UV Multiphoton Ionization Research Articles

High resolution energy-time of flight spectrometer: Dehydrogenation of fluorene cation as case study

Testing and performance validation of a new multipurpose time-of-flight mass spectrometer followed by an energy analyzer is presented. The instrument with high mass and energy resolution is primarily designed to study cations of polycyclic aromatic hydrocarbons (PAHs) and their dehydrogenation process. The energy correlated time-of-flight measurement is supplemented by Monte Carlo simulation to probe the dehydrogenation process in a relatively small PAH cation. The experiment is carried out on fluorene+ on a timescale of several microseconds. Fluorene cations with high internal energies were produced using UV multiphoton ionization. Specific n-photon processes leading to ionization as well as H-loss reaction were identified. The average value of dehydrogenation rate is estimated by fitting the measured data to the outcome of simulations. The quantification of H loss decay rate is in agreement with previously reported decay rate measurement. This corresponds to the internal energy available by inner valence electron emission caused by three photon process. The effectiveness of the instrument to access a range of decay rates (103–107 s−1) in a single measurement is demonstrated.

IR wavelength-selective laser desorption via O [sbnd]H and C [sbnd]H stretching modes

We present new results on wavelength-selective desorption of solid samples using the resonant interaction between the laser beam and the bulk. The experimental set-up is based on the coupling of three techniques: laser desorption in the near-infrared (IR) (2.7–4 μm) with a tunable IR optical parametric oscillator (OPO), UV multi-photon ionization, and reflectron time-of-flight mass spectrometry. The resonant character of the laser desorption process has been investigated for an ice/polycyclic aromatic hydrocarbon (PAH) mixture, by excitation of the O H and C H stretching modes. Highly preferential desorption has been evidenced, with exclusive desorption of water and PAH molecules at the O H and C H resonances, respectively. Potential analytical (e.g. selective analysis of complex samples) and technological (e.g. dry laser cleaning, DLC) applications are discussed.

Formation and measurement of cluster beams at gasdynamic cooling of CF2HCl molecules

The clustering of CF2HCl (Freon-22 refrigerant) molecules is found to take place when these molecules are dynamically cooled in a pulsed supersonic beam. A method of CF2HCl cluster beam diagnostics is developed that combines UV multiphoton ionization, time-of-flight mass spectroscopy, and cluster IR photodissociation. The velocity of directed motion of (CH2HCl)n clusters, as well as the longitudinal and transverse velocities of their thermal motion, are measured at different stagnation pressures P 0. The cluster mean size and the degree of clustering in the flow are estimated depending on supersonic flow conditions.

Photo-excited desorption of multi-component systems: Application to chalcogenide glasses

This work presents a laser desorption study of Ga 5Ge 20Sb 10S 65 chalcogenide glasses. The desorption products have been analyzed by UV multi-photon ionization and time-of-flight mass spectrometry. Desorption mechanisms and plume dynamics have been investigated by studying the desorption products velocity distribution profiles in the frame of a Knudsen layer model. A peculiar behavior (broadening of the mass spectral lines) of the Ga component was found at high desorption–ionization delays and a tentative explanation has been proposed, based on the very different thermal properties of the sample constituents.

The Electronic Spectrum of Methyleneimine

Cavity ring-down spectroscopy (CRDS) has been employed to observe the electronic spectrum of methyleneimine (H2CNH), which is the simplest imine compound. This species was prepared by the pyrolysis of methyl azide. The CRDS signals over the wavelength range 234 to 260 nm were recorded as a function of the temperature of a heated section of tubing upstream of the CRDS cell. The absorption spectrum of methyleneimine was found to be broad and structureless, with an absorption maximum near 250 nm. The absorption cross section of methyleneimine was estimated by comparison with the absorption spectrum of methyl azide. The 118-nm 1-photon photoionization and the UV multiphoton ionization mass spectra of a molecular beam of unpyrolyzed and pyrolyzed methyl azide were also investigated. The strongest mass peak in the multiphoton ionization of methyleneimine was found to be m/e = 28, corresponding to H2CN+ or HNCH+. These results are used to interpret the excited electronic states and photochemistry of methyleneimine.

The formation and characterization of freon 22 cluster beams

Freon 22 (CF2HCl) clusters have been found upon gasdynamic cooling of these molecules in a pulsed supersonic beam. A method for diagnostics of the cluster beams of freon 22 has been developed based on the phenomenon of UV multiphoton ionization in combination with the time-of-flight mass spectrometry and the IR photodissociation of clusters. The velocities of directed motion and the longitudinal and transverse velocity components of the thermal motion of (CF2HCl)n clusters in a beam of freon 22 were measured for various stagnation pressures P0. The degree of beam clusterization was estimated.

Resonant desorption of ice with a tunable LiNbO 3 optical parametric oscillator

We report on the use of a pulsed tunable mid-infrared optical parametric oscillator (OPO) for the IR resonant desorption of ice in the 3 μm range. Desorbed neutrals are detected by UV multi-photon ionization and time-of-flight mass spectrometry. Desorption yield is found to increase linearly with the OPO pulse energy in the 0–3 mJ range. The resonant character of the desorption process is very clearly evidenced by the study of the wavelength dependency of the desorption yield. The desorption spectrum peaks at 3.1 μm and is in remarkable agreement with the absorption spectrum of crystalline ice at T=100 K. This result differs from previous experiments using NIR macro-pulses of a free electron laser. The velocity distribution of the desorption products reveals the presence of at least two components. The fast component is consistent with our previous results obtained on doped ices and indicates a phase explosion process. The observation of high- n (H 3O) +(H 2O) n clusters is also reported.

Synthesis, separation, characterization, fragmentation, and aggregation of giant fullerenes

We have performed mass spectrometric studies of giant fullerenes. These fullerenes consist of even-numbered closed carbon shells and have been extracted from carbon soot produced in a carbon-arc source. By utilizing designed extraction techniques, the mass distributions can be made to peak near m/z ≈ 2500 u. The distribution are studied using laser-desorption mass spectrometry (time-of-flight and Fourier transform), detecting positive ions, negative ions, and neutral molecules. The neutral species are detected using UV multiphoton ionization and VUV single-photon ionization of laser-desorbed species. Additionally, giant fullerenes can be prepared selectively in the gas phase by laser desorption of phase-pure C 60. The results of the present study are compared with previous mass spectrometry experiments of giant fullerenes.

Excited state-selected transition metal cations from one-color UV multiphoton ionization

We have used one-color, resonance enhanced multiphoton ionization in the near-UV to create selectively the first excited terms of the transition metal ions Fe+, Ti+, and V+ in the gas phase. The term and level distributions of the resulting photoions are measured using time-of-flight photoelectron spectroscopy. We generally find better electron configuration and term selectivity for two-photon ionization via 4p resonant Rydberg levels than was found in previous work on three-photon ionization of 5s Rydberg levels. In certain Fe cases, a single ion total angular momentum level dominates the photoelectron spectrum. The simple picture of the 4p Rydberg levels as consisting of an ion core of well defined Lc–Sc and Jc weakly coupled to a Rydberg electron is remarkably useful. Deviations from this simple picture are discussed in terms of configuration interaction of resonant states and autoionizing structure in the continuum. The results will find application in studies of state-selected metal ion chemistry.

ChemInform Abstract: Neutral Metal Cluster Formation and Oxidation Reactions in the Photolysis of Iron Carbonyl van der Waals Complexes.

AbstractIron Clusters (Fex) and iron Cluster carbonyls (Fe"(CO)y) are produCed by UV multiphoton ionization of [Fe(CO)5]N Complexes prior to photoionization.

ChemInform Abstract: DISSOCIATION OF BENZYLAMINE IONS FOLLOWING INFRARED MULTIPLE PHOTON ABSORPTION, ELECTRON IMPACT IONIZATION, AND UV MULTIPHOTON IONIZATION

Chemischer InformationsdienstVolume 14, Issue 33 Preparative Organic Chemistry ChemInform Abstract: DISSOCIATION OF BENZYLAMINE IONS FOLLOWING INFRARED MULTIPLE PHOTON ABSORPTION, ELECTRON IMPACT IONIZATION, AND UV MULTIPHOTON IONIZATION J. H. CATANZARITE, J. H. CATANZARITESearch for more papers by this authorY. HAAS, Y. HAASSearch for more papers by this authorH. REISLER, H. REISLERSearch for more papers by this authorC. WITTIG, C. WITTIGSearch for more papers by this author J. H. CATANZARITE, J. H. CATANZARITESearch for more papers by this authorY. HAAS, Y. HAASSearch for more papers by this authorH. REISLER, H. REISLERSearch for more papers by this authorC. WITTIG, C. WITTIGSearch for more papers by this author First published: August 16, 1983 https://doi.org/10.1002/chin.198333104AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue33August 16, 1983 RelatedInformation

The dissociation dynamics of state selected metastable aniline ions by single and multiphoton ionization

The lifetimes with respect to dissociation of state selected aniline ions have been investigated by photoion–photoelectron coincidence. Lifetimes between 0.3 and 100 μs have been found when the aniline ion is prepared in energies ranging from 13.6 to 12.6 eV, respectively. These lifetimes are in good agreement with those of a recent study by Proch, Rider, and Zare, who observed metastable aniline ions in a UV multiphoton ionization (MPI) study in which three photons were required to reach the metastable ion energy range. By contrast, our visible MPI study of aniline shows no evidence for long-lived ions. This paradox is resolved by postulating that under the UV MPI conditions, a radiationless transition to the ground electronic state allows the 13 eV ions time to dissociate slowly, while under the much higher photon intensities needed in the visible MPI study, rapid up pumping of the excited ions prevents radiationless transitions. A lower limit for the radiationless transition rate of 2×108 s−1 is derived.

Visible and UV multiphoton ionization and fragmentation of polyatomic molecules

It is now known that tunable dye laser light leads to resonance enhanced photoionization of molecules in a mass spectrometer via multiphoton absorption. In some cases this process also leads to ion fragmentation. Time delayed tandem laser pulses of different wavelengths are employed to study the mechanism of this multiphoton ionization and fragmentation process in benzene. The experimental results strongly indicate that excitation does not proceed up an autoionization ladder of the neutral molecule, rather the multiphoton process is shown to be due to the climbing of two independent ladders, one up to the ionization potential in the neutral molecule, the second in the new species of molecular parent ions produced. Hence multiphoton ionization could also form a new basis of ion spectroscopy.