Multiphoton absorption is an intensity dependent nonlinear effect related to the excitation of virtual intermediate states. In the present work, multiphoton ionization and dissociation of the formic acid molecule (HCOOH) by the interaction with photons from 532 Nd: YAG laser at different intensities are discussed, using different carrier gases. The induced fragmentation-ionization patterns show up to 17 fragments and dissociation channels are proposed. Some evidence of small clusters formation and conformational memory from the ratio of the detected products, CO+ and CO2+, on the light of the available results, it is possible to conclude that they arise from trans and cis formic acid. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed. Following the Keldysh description it is possible, from our experimental parameters, characterize our results, in the multiphoton absorption regime.

We carry out experiments on the fragmentation of nitromethane by multiphoton absorption at the wavelength 266 nm. This was conducted in a reflectron (Jordan), modified in the laboratory. Due to the large number of fragments, special care has been taken into the calibration of the system, in the simultaneity between the laser pulse and the sample, and the associated electronics to ensure that produced fragment spectra arise from the interaction laser-sample. We emphasize the next aspects of the method: • Simple design for introducing a gas sample at laser interaction region to facilitate the cluster formation • Astonishing number of fragments produced by multiphoton absorption.

Time of flight laser photoionization has been used to study the response of some molecules of biological interest under laser radiation. One of the questions of great interest today is the effect of radiation on DNA and RNA molecules. Damage to these molecules can be caused directly by radiation or indirectly by secondary electrons created by radiation. As response of the radiation field fragmentation process can occur producing different ions with kinetic energies of a few electron volts. In this paper we present the results of the interaction of 355nm laser with the nitrogen bases adenine(A) and uracil(U) using time-of-flight spectrometry and the comparison of experimental results on the effects of laser radiation in (A) and (U) belonging to two different ring groups, purines and pyrimidines respectively,which are linked to form the AU pair of the RNA.

Dissociation and ionization of adenine and uracil were investigated in the multiphoton absorption regime using laser pulse at 355nm in conjunction with TOF mass spectrometry in reflectron mode (R-TOF). In contrast of previous investigations where a notorious amount of low mass ions was detected arising from both molecules.

We present a detailed Langmuir probe, optical emission spectroscopy (OES), and quadrupole mass spectrometry (QMS) characterization of a DC CO2–H2 plasma mixture, complemented by calculations of the electron energy distribution functions (EEDFs) and ionization rates of CO2 plasma with varying H2 ratios using Boltzmann equation (BE) solver BOLSIG+, assuming a bi-Maxwellian distribution. Both the measured and calculated EEDFs as a function of the H2 concentration agreed well and showed a bi-Maxwellian distribution. The measured and calculated electron temperatures Te as a function of the increment in the H2 concentration (0–100%) increased in the range of 2.5–3.1 eV. The measured and calculated electron densities (Ne) as a function of H2 concentration exhibited the same increasing behavior (approximately 1010 cm−3), which confirms that the mixture composition directly influences the plasma-related parameters and results in a large fraction of H atoms by reaction e + H2 → H + H. An ascending Te would result in higher ionization rates (explaining the observed increase in electron densities), which agrees with the ionization rate behavior obtained by the BE calculation. Both OES and QMS techniques detected the species H (through the lines Hα, Hβ, and Hγ), CO, CO2, CO2+, O2, OH, O, C2, CO, and CO+. An analysis of the CO/CO2 and O2/CO2 ratios would clarify that OH is formed from O2 + H → OH + O rather than other reactions involving CO species. At a 100% CO2 concentration, CO and O2 formations proceed in accordance with the stoichiometry of 2CO2 → 2CO + O2.

High-resolution mass spectrometry using the time of flight (TOF) technique with a reflectron with multiphoton absorption was used to analyze the fragmentation pattern of nitromethane in a collision-free system. We used a radiation source with nanosecond laser pulses of 532 nm, 355 nm, and 266 nm wavelengths and a supersonic jet of nitromethane to produce positive fragment ions. The density power (irradiation) range was from 109 to 1010 W/cm(2). The identification of 20 ions at a wavelength of 532 nm was obtained, whereas at 266 nm, more than 60 fragment ions were identified, as was the parent ion and many clusters. We associate these ionic fragments as a function of the intensity, energy, and pulse duration of the radiation source. The observation of radicals such as CH1,2,3, C2H1,2,3, C3H1,2,3, and CH3O, CHNO, higher mass molecules, and clusters is presented. The absence of the parent ion at 532 nm and 355 nm wavelengths demonstrates that the ladder switching mechanism elucidates the dissociation-ionization (DI) pathways of nitromethane. At 266 nm, the presence of the parent ion and the clusters are an indication of the functioning of the other model of fragmentation (ID). Due to the experimental characteristics, the numerous fragments seem to be a result of the interactions of the intensity of the electromagnetic radiation over nitromethane in the gas phase and their clusters. (C) 2019 Published by Elsevier B.V.

Relative cross sections for the valence shell photoionisation (PI) of S-2 ground level and 2D metastable Ca+ ions were measured with high energy resolution by using the ion-photon merged-beams technique at the Advanced Light Source. Overview measurements were performed with a full width at half maximum bandpass of Delta E = 17 meV, covering the energy range 20-56. eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of Delta E = 3.3 meV. The photon energy scale was calibrated with an uncertainty of +/- 5. meV. By comparison with previous absolute measurements the present experimental high-resolution data were normalized to an absolute cross-section scale and the fraction of metastable Ca+ ions that were present in the parent ion beam was determined to be 18% +/- 4%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the closecoupling expansion were performed for the Ca+(3s(2)3p(6)4s S-2(1/2)) and Ca+(3s(2)3p(6)3d D-2(3/2,5/2))levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.

We present the experimental results from ionization and dissociation by multiphoton absorption (MPI) of uracil and a mixture of uracil with Ar using a Reflectron time of flight spectrometer along with radiation from 355 nm at pulsed Nd:YAG laser . We focus on the light ions production. The MPI mass spectra show that the presence and intensity of the resulting ions depend on the density power of the laser. The resulting ions in the mass spectra are identified and found similar behavior in the case of H+ and C+ as when multiple charged ions are used. Different results were found in contrast with those, recently reported, when electrons or photons of other wavelength were used. The number of 355nm absorbed photons was calculated accordingly to Keldysh theory and similar results were fond using pure uracil or uracil-Ar mixture. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed.

The experimental results from the interaction of a sample of acetaldehyde (CH3 CHO) with laser radiation at intensities between 10(9) and 10(11) Wcm(-2) and wavelengths of 266 and 355 nm are reported. As a result of multiple photon absorption, cations from ionization-dissociation (I-D) or dissociation-ionization (D-I) processes, were detected using a reflectron time of flight mass spectrometer. The processes I-D is predominant at 355 nm and D-I is predominant at 266 nm. The formation of different ions is discussed. From analysis of the ratios between the ion currents [I(CH3CO+)+I(CO+)]/[I(CH3+)+I(HCO+)], originated from the C-C bond or from the C-H bond breaking at different laser intensities, the predominant channels are determined.

Dissociation and ionization of formic acid was investigated by multiphotonic absorption regime using laser pulse at 355nm in conjunction with TOF mass spectrometry in reflectron mode (R-TOF). From the different type of detected fragment ions is inferred the formation of some small clusters of formic acid.

Using VUV radiation several ionic fragments were observed from the multiphoton dissociation of the Nitromethane. The detection of the molecular ions was focused on: HCO+, NO+, CNOH+ and CH3+ due to their importance in reactions involving the formation of molecules in the interstellar clouds and the surrounding regions of the stars.

The cooled molecular beams of acenes compounds as naphthalene C10H8, anthracene C14H10, and benzantracene C18H12, were produced by adiabatic expansion in high vacuum chamber, 10(-8) torr. Molecular beams interacted with laser radiation of 266 and 355 nm, from a Ng:YAG laser at intensities up to 10(10) W.cm(-2). At higher intensities the multiple photon absorption was possible. The number of photons was calculated using Keldysh approach. The dominant photophysics of photon-molecule interactions were photodissociation and photoionization processes depending on the wavelength used during the experiment.

The absolute single-photoionization cross section was measured for Cl-like K2+ over the photon energy range from 44.2 to 69.7 eV at a constant energy resolution of 0.045 eV. The experiments were performed by merging an ion beam with a beam of synchrotron radiation from an undulator. The ground-state ionization threshold was measured at 0.004-eV energy resolution to be 45.717 +/- 0.030 eV. The measurements are rich in resonance structure due to multiple Rydberg series of transitions to autoionizing states. These series are assigned spectroscopically using the quantum defect method, guided by pseudorelativistic Hartree-Fock calculations for the energies and oscillator strengths of transitions to autoionizing states. The experimental results, which include significant contributions from K2+ ions initially in metastable states, are in satisfactory agreement with a linear superposition of semirelativistic R-matrix calculations of photoionization cross sections from these initial states.

Experimental studies have been carried out for nanosecond 266-nm laser-induced photoionization and dissociation of fluoranthene, C16H10 with pulse energies from 0.5 to 20 mJ using a time of flight mass spectrometer. The fragmentation patterns have been characterized and discussed with respect to the number of absorbed photons. They fall into three regimes. The first regime involves low energy processes. where the molecular parent ion promptly dissociates, resulting in the formation of CmHn+(m = 11 - 15) by a process where up to two photons are absorbed. The second regime involves intermediate energy, where dissociative processes are activated by up to three-photon absorption and produce a second group of daughter ions: C10Hn+, C9Hn+ and C8Hn+. Finally, there is a third dissociative process, characterized by the absorption of up to four photons, producing C7Hn+, C6Hn+, C5Hn+, C4Hn+, and C3Hn+. Most of the detected ions are of the form CmHn+ with m < n. Total deprotonation has also been observed. The mechanism proposed involves the dissociation of the parent ion, which then dissociates by different competitive channels. Helium, neon and argon were used as carrier gases (CG). A detailed discussion is presented regarding the use of He as the CG. The laser pulse intensity allows the absorption of up to nine photons, observed through the formation of multiply charged ions of some of the CG atoms. (C) 2012 Elsevier B.V. All rights reserved.

The photodissociation (PD) and photoionization (PI) of 1,4-pentadiene (PDE), which result in the absorption of multiple photons, were studied both experimentally and theoretically. The PD and PI ions were the result of the interaction of a cooled molecular beam of PDE with laser radiation of wavelengths 266 and 355?nm, measured using a time of flight (TOF) mass spectrometer. There are several differences in the ionization patterns, with the wavelength as a common characteristic in the absence of the parent ion, and on the possible dissociation of the neutral species such as C2H3 and C3H5, which then dissociates and ionizes. To interpret the results, the potential energy surface (PES) of PDE was calculated. Using time-dependent density functional theory (TD-DFT), the excitation energies and potential energy surfaces along the two main dissociative coordinates, namely, C2C3 and C3H, were also calculated. Possible mechanisms responsible for the formation of the observed ions are proposed: hydrogen loss, molecular hydrogen formation, simple CC dissociation, total deprotonation and hydrogen transposition.

Laser interaction whitthe gas phase nucleobase adenine is studied. A linear TOF mass spectrometer is utilized for measurements that require high mass resolution, high sensitivity, and sufficient ion yields of low mass fragment cations. The ion mass spectra are discussed at different laser energy intensities and two temperatures. In contrast to previous studies a number light ion is present in the mass spectra. The ion formation curves for 23 different ions are measured for the laser energy range from about 109 to 1010 W cm–2 and masses between 1 and 43 besides mass 57 which was present in the mass spectra and will be discuss. Data were taken heating the sample at 235 Co. The number of 355nm absorbed photons was calculated accordingly to Keldysh theory and similar results were found using adenine -Ar mixture. Our results are compared with those reported formed by protons, electrons or multiple charged ions interactions. Different ions were found indicating the possible effect of multiphoton absorption.

Experimental evidence is presented for confinement resonances predicted in photoionization of the endohedral Xe@C-60(+) molecular ion at photon energies corresponding to the giant 4d resonance of Xe.