Multiphoton ionisation and dissociation of NO2 by 50 fs laser pulses

Singhal, R.P.; Kılıç, Hamdi Şükür; Ledingham, K.W.D.; Kosmidis, C.; McCanny, T.; Langley, A. J.; Shaikh, W.

doi:10.1016/0009-2614(96)00226-6

Cited by 38 publications

(46 citation statements)

References 17 publications

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“…The insets show this to be a weaker effect in the 375 nm spectrum despite increased fragmentation at the neighbouring C 3 and C 4 fragment groups. The peaks at m/z 46.5 and 46, within experimental error, show the correct 13 C/ 12 C isotopic ratio for a molecule with seven carbon atoms ($8%).…”

Section: Resultsmentioning

confidence: 84%

“…At a wavelength of 750 nm, exclusive parent production can be achieved at higher intensities ($3-5 Â 10 13 possible to match the 375 nm beam intensities with the highest intensities of the 750 nm beam, but comparing similar laser beam fluxes over the intensity range studied, fragmentation is clearly seen to be more prominent with the UV wavelength. Daughter ion formation can thus be suppressed to a greater relative degree at 750 nm.…”

Section: Resultsmentioning

confidence: 87%

“…Schutze et al 22,23 have applied non-resonant multiphoton ionization (NRMPI) to semiconductor materials such as GaAs. Using a technique known as picosecond laser desorption mass spectrometry (ps-LDMS) at beam intensities around 10 13 W cm À2 , they showed that the same degree of ionization for all species under investigation was possible in the saturation regime, and indicated that standard-free sensitive surface quantification could be achieved. The general application of laser mass spectrometry to aromatic molecules has been extensive, with particular emphasis on the prototype molecule benzene.…”

Section: à2mentioning

confidence: 98%

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Time-of-flight mass spectrometry of aromatic molecules subjected to high intensity laser beams

Smith

Ledingham

Singhal

et al. 1998

Rapid Commun. Mass Spectrom.

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The recent introduction of femtosecond technology to pulsed lasers has led to the development of femtosecond laser mass spectrometry (FLMS). The present paper describes an FLMS investigation of the aromatic molecules, benzene, toluene and naphthalene. Wavelengths of 750 and 375 nm were used with beam intensities up to 4 Â 10 14 W cm À2 . Pulse widths were of the order of 50-90 fs. The laser system was coupled to a linear time-of-flight mass spectrometer. This experimental method of chemical analysis is gaining momentum, often replacing its nanosecond forerunner, resonant enhanced multiphoton ionization. For the said molecules, predominant parent ion production is found, making identification unambiguous. In fact this characteristic is being consistently attained in small to medium mass molecules irradiated under similar conditions, leading to the conclusion that a universal chemical detection system is a possibility. Such soft ionization is particularly evident at longer wavelengths ($750 nm) with less relative fragmentation, daughter ion formation, compared to results at shorter wavelengths ($375 nm). In terms of parent ion formation, similar numbers are produced with laser intensities around 10 14 W cm À2 for both wavelengths. It has also been shown that at a threshold of about 5 Â 10 13 W cm À2, double ionized molecules appear for the 750 nm wavelength. These interesting new mass spectra display intense single, double and even triple ionized peaks without significantly increased dissociation. Such effects are less pronounced at 375 nm.

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Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 87%

Section: à2mentioning

confidence: 98%

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Time-of-flight mass spectrometry of aromatic molecules subjected to high intensity laser beams

Smith

Ledingham

Singhal

et al. 1998

Rapid Commun. Mass Spectrom.

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“…The dominant dissociative multiphoton pathway was identified being a three photon excitation to a repulsive potential energy surface correlating to NO͑C 2 ⌸͒ +O͑ 3 P͒ followed by a one photon ionization to yield NO + ͑X 1 ⌺ + ͒ +O͑ 3 P͒. Singhal et al 24 showed that with the same color laser light, 375.3 nm, but shorter pulses of about 50 fs, the NO + fragment was created via dissociation of NO 2 in the first excited state followed by three-photon ionization of the neutral NO͑X 2 ⌸͒ fragment. Two color femtosecond pump-probe spectroscopy in combination with fluorescence detection has been employed by López-Martens et al 25 The NO 2 molecule was excited at 400 nm and the dissociation products were detected by dispersed fluorescence.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond time-resolved photoelectron-photoion coincidence imaging of multiphoton multichannel photodynamics in NO2

Vredenborg¹,

Roeterdink²,

Janssen³

2008

The Journal of Chemical Physics

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The multiphoton multichannel photodynamics of NO 2 has been studied using femtosecond time-resolved coincidence imaging. A novel photoelectron-photoion coincidence imaging machine was developed at the laboratory in Amsterdam employing velocity map imaging and "slow" charged particle extraction using additional electron and ion optics. The NO 2 photodynamics was studied using a two color pump-probe scheme with femtosecond pulses at 400 and 266 nm. The multiphoton excitation produces both NO 2 + parent ions and NO + fragment ions. Here we mainly present the time dependent photoelectron images in coincidence with NO 2 + or NO + and the ͑NO + , e͒ photoelectron versus fragment ion kinetic energy correlations. The coincidence photoelectron spectra and the correlated energy distributions make it possible to assign the different dissociation pathways involved. Nonadiabatic dynamics between the ground state and the A 2 B 2 state after absorption of a 400 nm photon is reflected in the transient photoelectron spectrum of the NO 2 + parent ion. Furthermore, Rydberg states are believed to be used as "stepping" states responsible for the rather narrow and well-separated photoelectron spectra in the NO 2 + parent ion. Slow statistical and fast direct fragmentation of NO 2 + after prompt photoelectron ejection is observed leading to formation of NO + + O. Fragmentation from both the ground state and the electronically excited a 3 B 2 and b 3 A 2 states of NO 2 + is observed. At short pump probe delay times, the dominant multiphoton pathway for NO + formation is a 3 ϫ 400 nm+ 1 ϫ 266 nm excitation. At long delay times ͑Ͼ500 fs͒ two multiphoton pathways are observed. The dominant pathway is a 1 ϫ 400 nm+ 2 ϫ 266 nm photon excitation giving rise to very slow electrons and ions. A second pathway is a 3 ϫ 400 nm photon absorption to NO 2 Rydberg states followed by dissociation toward neutral electronically and vibrationally excited NO͑A 2 ⌺ , v =1͒ fragments, ionized by one 266 nm photon absorption. As is shown in the present study, even though the pump-probe transients are rather featureless the photoelectron-photoion coincidence images show a complex time varying dynamics in NO 2 . We present the potential of our novel coincidence imaging machine to unravel in unprecedented detail the various competing pathways in femtosecond time-resolved multichannel multiphoton dynamics of molecules.

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“…In addition, at 795 nm and a power density of 3.5 ϫ 10 14 W/cm 2 , the presence of a competition between multiphoton ionization (MPI) and Coulomb explosion (CE) channels is revealed by peak shape analysis, and is thought to be operative under these conditions for all of the molecules investigated. [5][6][7][8][9][10][11][12], and polyatomic aromatic organic molecules [13][14][15][16][17][18][19][20][21][22][23], has been the subject of intense investigation. These studies have focused on the fundamental interaction of the laser pulse with the atomic or molecular system, and have generally found a number of operative ionization and dissociation mechanisms present, which are sensitive to the laser wavelength and power density.…”

mentioning

confidence: 99%

Femtosecond laser photoionization time-of-flight mass spectrometry of nitro-aromatic explosives and explosives related compounds

Mullen

Coggiola

Oser

2009

J. Am. Soc. Mass Spectrom.

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The ultrafast laser-induced photoionization and photodissociation processes of the nitroaromatic containing explosive and explosive related compounds (ERCs) nitrobenzene (NB), 1,3-dinitrobenzene (DNB), m-nitrotoluene (MNT), 2,4-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT) have been investigated at three laser wavelengths and power densities using a time-of-flight mass spectrometer. Examination of the mass spectra of these compounds reveals the enhanced formation of the molecular ion [M ϩ ] when ultraviolet (332 nm) and visible (495 nm) light is used relative to infrared (795 nm) radiation. In addition, at 795 nm and a power density of 3.5 ϫ 10 14 W/cm 2 , the presence of a competition between multiphoton ionization (MPI) and Coulomb explosion (CE) channels is revealed by peak shape analysis, and is thought to be operative under these conditions for all of the molecules investigated. [5][6][7][8][9][10][11][12], and polyatomic aromatic organic molecules [13][14][15][16][17][18][19][20][21][22][23], has been the subject of intense investigation. These studies have focused on the fundamental interaction of the laser pulse with the atomic or molecular system, and have generally found a number of operative ionization and dissociation mechanisms present, which are sensitive to the laser wavelength and power density. In addition, a number of studies have also been dedicated to the investigation of the analytical usefulness of femtosecond laser ionization toward molecular specific detection. A prime example is the application to the ionization and detection of the explosives and explosives related compounds pioneered by . Their studies focused on an understanding of the mass spectra obtained using ultrafast laser pulses in conjunction with time-of-flight mass spectrometry, M ϩ ion formation, and specific molecular fragments that could be assigned to a particular precursor species. Of particular interest was the demonstration of isomer dependent mass spectra for the three isomers of nitrotoluene.The motivation to apply femtosecond laser ionization to the study of explosives and ERCs originated from previous laser ionization work, which found that nanosecond laser ionization in the ultraviolet led to extensive molecular fragmentation [31][32][33][34][35][36]. The extensive fragmentation was determined to be non-useful for species-specific identification, even though abundant NO ϩ ions were observed in the mass spectra [37]. The presence of NO ϩ in the mass spectra of these species naturally raised questions regarding its formation. Mechanistically, it was discovered that the dissociative lifetimes of the intermediate states involved in the ionization process were about a few hundred femtoseconds, and that this rapid dissociation led to the extensive fragmentation observed in the mass spectra. Further, the presence of NO ϩ in the mass spectra of these species was attributed to rapid dissociation of the parent molecule (RNO 2 ) producing the NO 2 fragment. The NO 2 molecule undergoes an additional photon absorptio...

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Multiphoton ionisation and dissociation of NO2 by 50 fs laser pulses

Cited by 38 publications

References 17 publications

Time-of-flight mass spectrometry of aromatic molecules subjected to high intensity laser beams

Time-of-flight mass spectrometry of aromatic molecules subjected to high intensity laser beams

Femtosecond time-resolved photoelectron-photoion coincidence imaging of multiphoton multichannel photodynamics in NO2

Femtosecond laser photoionization time-of-flight mass spectrometry of nitro-aromatic explosives and explosives related compounds

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