Resonance enhanced multiphoton dissociation of polycyclic aromatic hydrocarbons cations in an RF ion trap (original) (raw)
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Physical Review A
The photoprocessing of astrophysically relevant small polycyclic aromatic hydrocarbon (PAH) molecules, namely, anthracene, phenanthrene, and pentacene, under intense UV field is experimentally studied to explore the formation of smaller ions upon their dissociative ionization and the effect of their size and structure on the dynamics of dissociative ionization. The molecules are UV processed in the multiphoton regime using a 266-nm nanosecond laser pulse. The dissociative ionization spectra at different laser intensities reveal distinct dissociation dynamics of these PAHs based on their size and structures.
Multiphoton ionization and dissociation of naphthalene at 266, 355, and 532 nm
Journal of Photochemistry and Photobiology A-chemistry, 2010
A comparison of laser-induced multiphoton ionization/dissociation and dissociation/ionization pathways of naphthalene, C 10 H 8 , is presented at 266, 355, 532 nm, using time-of-flight mass spectrometry, ToF-MS. From the spectra several processes were identified: molecular ionization, simple dissociation, hydrogen transposition, hydrogen loss, and total deprotonation. The dependence on the wavelength and the radiation intensity is clear. At 266 nm energies per pulse, <1.0 mJ (9.23 × 10 2 MW cm −2 ), C 10 H 8 + dominates the spectra and new ions were observed as the laser intensity was increased. At 355 nm, hydrogen loss was the principal dissociative route, with the formation of low mass ions: CH n + , 0 < n < 6, in particular CH 6 was identified by isotopic analysis. At 532 nm, the C n H m + ions, 2 < n < 5, were the most abundant species. The calculated numbers of absorbed photons along with previous calculations were used to propose different fragmentation channels.
Review of Scientific Instruments, 2005
A Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been installed at a free electron laser (FEL) facility to obtain infrared absorption spectra of gas phase ions by infrared multiple photon dissociation (IRMPD). The FEL provides continuously tunable infrared radiation over a broad range of the infrared spectrum, and the FT-ICR mass spectrometer, utilizing a 4.7 Tesla superconducting magnet, permits facile formation, isolation, trapping, and high-mass resolution detection of a wide range of ion classes. A description of the instrumentation and experimental parameters for these experiments is presented along with preliminary IRMPD spectra of the singly-charged chromium-bound dimer of diethyl ether ͑Cr͑C 4 H 10 O͒ 2 + ͒ and the fluorene molecular ion ͑C 13 H 10 + ͒. Also presented is a brief comparison of the fluorene cation spectrum obtained by the FT-ICR-FEL with an earlier spectrum recorded using a quadrupole ion trap (QIT).
Rapid Communications in Mass Spectrometry, 2019
Rationale: Methods for isomer discrimination by mass spectroscopy are of increasing interest. Here we describe the development of a 3D ion trap for Infrared Multiple Photon Dissociation (IRMPD) spectroscopy that enables the acquisition of the infrared spectrum of selected ions in the gas phase. This system is suitable for the study of myriad chemical systems, including isomer mixtures. Methods: A modified 3D ion trap was coupled to a CO2 laser and an OPO/OPA system operating in the 2300 to 4000 cm-1 range. DFT vibrational frequency calculations were carried out to support spectral assignment. Results: Detailed descriptions of the interface between the laser and the mass spectrometer, the hardware to control the laser systems, the automated system for IRMPD spectrum acquisition and data This article is protected by copyright. All rights reserved. management are presented. The optimization of the crystal position of the OPO/OPA system to maximize the spectroscopic response under low power laser radiation is also discussed. Conclusions: OPO/OPA and CO2 laser-assisted dissociation of gas ions were successfully achieved. The system was validated by acquiring the IRMPD spectra of model species and comparing with literature data. Two isomeric alkaloids of high economic importance were characterized to demonstrate the potential of this technique, which is now available as an open IRMPD spectroscopy facility in Brazil.
Applied Surface Science, 2007
Characterization of polycyclic aromatic hydrocarbons (PAHs) samples has been performed by laser desorption combined with multi-photon ionization technique using two different geometries of the ionization laser beam. This comparative study evidences the strong influence of ionization laser fluence on PAH fragmentation. Through a $10 3 enlargement of the ionization probe volume and 10 4 reduction of laser fluence over previous studies, fragment free mass spectra are obtained with higher sensitivity and selectivity. The ability to measure fragment free PAH mass spectra is a very important step in the end goal of measuring complex unknown mixtures of PAH desorbed from solid surface such as soot samples. #
International Journal of Mass Spectrometry and Ion Processes, 1994
We have developed an improved method, dynamic r.f. trapping, for capturing laser desorbed ions in a quadrupole ion trap mass spectrometer (ITMS). Trapping efficiency is enhanced by over an order of magnitude over previous methods. A 308 nm excimer laser pulse desorbs the sample-trimethylphenylammonium iodide (TPA-I) is used in most of the work reported-from a probe inserted through the ring electrode. The laser is fired as the r.f. trapping potential (risetime about 175 ps) is applied to the ring electrode. Laser desorbed ions penetrate the trap while the trapping potential is low, but cannot escape because the r.f. potential rises substantially during their transit across the trap. The trapping efficiency is found to depend critically on the kinetic energy of the laser desorbed ions, and on the r.f. amplitude, phase, and rate of change of the r.f. amplitude when the laser fires. Cation and anion signals are recorded as functions of coarse and fine steps in the laser-to-r.f. timing. Coarse and fine timing steps test the effects of laser-to-r.f. delay and phase respectively. We also report effects on trapping efficiency of buffer gas pressure and composition (He neat versus He : Xe mixtures) and the amplitude of the ring electrode steady state r.f. potential. The delay and phase dependence of the experimental data is analyzed with reference to an effective potential barrier model. Differences in the phase and delay dependences for anions and cations are attributed to differences in Debye shielding early in the expansion of the laser desorbed plume. Cation and anion mass spectra are presented for laser desorption/ionization of TPA-I and pyrene. For TPA-I desorption, reactions between laser desorbed cations and neutral TPA fragments in the early, high density portion of the laser plume lead to production of high mass cations.
Laser desorption in a quadrupole ion trap. Mixture analysis using positive and negative ions
Analytical Chemistry, 1993
We demonstrate the generation of both negative and positive ions by laser desorption directly within a quadrupole ion trap and the application of this method to analyze complex samples containing compounds such as explosive residues, metal complexes, and polynuclear aromatic hydrocarbons. In some cases the ability to rapidly switch between positive and negative ion modes provides sufficient specificity to distinguish different compounds of a mixture with a single stage of mass spectrometry. In other experiments, we combine intensity variation studies\with tandem mass spectrometry experiments and positive and negative ion detection to further enhance specificity.
Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions
International Journal of Mass Spectrometry, 2006
In this review, we present an overview of our recent work on the infrared spectroscopy of mass-selected gas-phase molecular ions. The ions are stored and isolated in a quadrupole ion trap where they are investigated with infrared multiple photon dissociation spectroscopy using a free electron laser (FEL). The wide and continuous tunability of FELIX, the FEL for Infrared eXperiments at the FOM institute for Plasma Physics in The Netherlands, allows us to explore the interesting mid-infrared range between 500 and 2000 cm−1, sometimes referred to as the fingerprint region. The experiments have focused on polycyclic aromatic hydrocarbons because of their hypothesized occurrence in the interstellar medium, both in neutral and cationic forms. Furthermore, several related species of fundamental chemical interest have been investigated, such as molecular fragment ions and protonated species. The spectra are compared to theoretical spectra calculated at the density functional theory level. The effects of multiple photon excitation and dissociation dynamics on the appearance of the spectrum are extensively discussed. A mathematical model to account for the effects of anharmonicity is described. It explains for instance, qualitatively, how the observed spectral response can vary (slightly) with the fragment channel, which allows one to “direct” dissociation reactions in a non-coherent fashion by the choice of the infrared excitation wavelength.
International Journal of Mass Spectrometry, 2002
Nanosecond laser desorption/femtosecond laser mass spectrometry (LD/FLMS) incorporating a reflectron time-of-flight mass spectrometer has been used to study the ionisation/fragmentation of polycyclic aromatic hydrocarbons (PAHs) in intense laser fields (7.0 × 10 14 to 9.3 × 10 15 W cm −2). Pulses of 80 fs, 800 nm have been used to post-ionise the PAHs anthracene, tetracene and pentacene. For each molecule strong singly and doubly charged parent ions are observed accompanied by fragmentation. In addition, strong triply charged parent ions (M 3+) are observed for anthracene and weaker M 3+ signals for tetracene and pentacene are also observed. Nanosecond post-ionisation (266 nm, 16 ns) spectra of the molecules have been recorded and are included for comparison with the femtosecond data. Similarities in the observed fragmentation pattern of low-mass fragments of the nanosecond and low intensity femtosecond spectra are highlighted. In addition, as the laser intensity increases, it is observed that fragmentation pathways preferentially switch from C m H 3 + ion yield to C m + production for m = 2-5 at a critical intensity which is molecule dependent.