scholarly journals Multiphoton Ionization/Fragmentation of SO2: Experimental and Computational Studies

1985 ◽  
Vol 5 (5) ◽  
pp. 239-255 ◽  
Author(s):  
M. Asscher ◽  
W. L. Guthrie ◽  
T.-H. Lin ◽  
N. Ohmichi ◽  
J. Silberstein ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Laser Power ◽  
Laser Intensity ◽  
Multiphoton Ionization ◽  
Branching Ratio ◽  
Computational Studies ◽  
Fragmentation Pattern ◽  
Power Curve ◽  
Parent Molecule ◽  
Ionic Fragmentation

The ionic fragmentation pattern of SO2 was measured as a function of laser power at the 223–220 nm wavelength range. The time of flight (TOF) mass spectrum shows essentially no parent ions. The principal ions observed were SO+ and mass 32. The fraction of S+ ions increases monotonically with increasing laser power while the fraction of SO+ which dominates at low powers reaches a maximum and falls below that of S+. The fraction of both ions changes nonlinearly with the laser intensity and tends to level off at the higher powers. The results are found consistent with a statistical (maximum entropy) computation of the fragmentation pattern. By comparing the observed (S+ + O2+)/SO+ branching ratio vs. laser power with the computed branching ratio vs. energy uptake per parent molecule one obtains an energy uptake vs. laser power curve. The results are discussed in terms of the possible dissociation/ionization pathways.

scholarly journals The Potential of Vacuum Ultraviolet Photoionization Mass Spectrometry in Monitoring Photofragmentation of Organometallics

1993 ◽  
Vol 13 (2) ◽  
pp. 113-119 ◽  
Author(s):  
S. Georgiou ◽  
E. Mastoraki ◽  
E. Raptakis ◽  
Z. Xenidi
Keyword(s):  
Molecular Beam ◽  
Vacuum Ultraviolet ◽  
Impact Ionization ◽  
Microwave Discharge ◽  
Fragmentation Pattern ◽  
Photoionization Mass Spectrometry ◽  
Vuv Photoionization ◽  
Ionic Fragmentation ◽  
Deposition Processes ◽  
Fragmentation Patterns

The paper examines the potential of vacuum ultraviolet (VUV) photoionization mass spectroscopy in probing the fragmentation of organometallics in molecular-beam studies and laser-assisted deposition processes. To this end, the ionic fragmentation pattern of few common organometallics, namely metallocenes and carbonyls, is examined at selected VUV wavelengths, produced by microwave-discharge resonance atomic lamps. Discussion of the recorded spectra in terms of the electronic structure of the compounds indicates lack of dynamical bias in the VUV photoionization/fragmentation of metal complexes. Excitation with VUV light results in simpler ionic fragmentation patterns than what observed with electron-impact ionization, thereby enabling accurate monitoring of the excimer-laser photodissociation of organometallics. Finally, the intensity of the VUV ionic signal appears to be adequate for molecular-beam studies. An illustrative example is provided for the study of the 248nm-induced photodesorption of Mo(CO)6 from cryogenic films.

Increased urinary excretion of analogs of Krebs cycle metabolites and arabinose in two brothers with autistic features

1995 ◽  
Vol 41 (8) ◽  
pp. 1094-1104 ◽  
Author(s):  
W Shaw ◽  
E Kassen ◽  
E Chaves
Keyword(s):  
Mass Spectrum ◽  
Citric Acid ◽  
Krebs Cycle ◽  
Response Factor ◽  
Fragmentation Pattern ◽  
Acid Analog ◽  
High Concentrations ◽  
Mass Shifts ◽  
Derivatives Of ◽  
Tms Derivatives

Abstract A marked increase in analogs of Krebs cycle metabolites was found in the urine of two brothers with autistic features. These metabolites included citramalic, tartaric (3-OH-malic), and 3-oxoglutaric acids and compounds tentatively identified as a citric acid analog and partially identified as a phenylcarboxylic acid by the fragmentation pattern of the trimethylsilyl (TMS) derivatives of the compounds and mass shifts of the same compounds derivatized with perdeuterated N,O-bis(trimethylsilyl)trifluoroacetamide. The molecular mass of the TMS derivative of the tentatively identified citric acid analog was 596 Da, based on a finding of a significant M - 15 ion at m/z 581. The citric acid analog was excreted in quantities as high as 137 mmol/mol creatinine, based on the response factor of citric acid as a surrogate calibrator. A carbohydrate with a retention time and mass spectrum identical to arabinose was also found in high concentrations in the urine of these brothers.

scholarly journals Multiphoton Ionization Mass Spectrometric (MPIMS) Study of Phenol: Mechanism of Ionic Fragment Formation

1983 ◽  
Vol 3 (1-6) ◽  
pp. 29-47 ◽  
Author(s):  
R. S. Pandolfi ◽  
D. A. Gobeli ◽  
Jonathan Lurie ◽  
M. A. El-Sayed
Keyword(s):  
Laser Pulse ◽  
Energy Levels ◽  
Multiphoton Ionization ◽  
Pulsed Laser ◽  
Ionic Species ◽  
Low Energy ◽  
Ionization Mass ◽  
Fragmentation Pattern ◽  
Dissociation Channel ◽  
532 Nm

Time of flight (TOF) mass spectrometry is used in conjunction with a variable repelling voltage technique to elucidate the mechanism by which phenol ionizes and dissociates under 266 nm pulsed laser irradiation in combination with a 532 nm or 355 nm pulsed laser. The results suggest that, like benzene, the molecular ion is the predominant precursor of all ionic species generated in the process. Predominance of C5Hx+ species at relatively low powers confirms the presence of a low energy dissociation channel involving the elimination of CO. The use of a second laser at 532 nm is found to selectively destroy the C5Hx+ (as compared to the parent ion) species. The parent ion is found to be protected from the radiation of the second laser pulse at 532 nm but not at 355 nm if the second laser pulse is delayed by 50 ns. This is explained in terms of relaxation within the parent ion energy levels, the location of a low energy dissociation channel and the wavelengths of the lasers used. The main aspects of the fragmentation pattern are discussed in terms of the statistical theory of Rebentrost and Ben-Shaul.

Non-adiabatic photodissociation dynamics of BrCl

1994 ◽  
Vol 72 (3) ◽  
pp. 758-761 ◽  
Author(s):  
Jianying Cao ◽  
Hans-Peter Loock ◽  
Charles X.W. Qian
Keyword(s):  
Laser Radiation ◽  
Potential Energy ◽  
Multiphoton Ionization ◽  
Branching Ratio ◽  
Tunable Laser ◽  
Branching Ratios ◽  
Excitation Wavelength ◽  
Dissociation Dynamics ◽  
Adiabatic Transitions ◽  
Insight Into

Nozzle-cooled BrCl was excited with tunable laser radiation at selected wavelengths between 389 and 500 nm. The chlorine atomic fragments in their Cl*(2P1/2) and Cl(2P3/2) state were stated-selectively probed by resonance-enhanced multiphoton ionization. The branching ratio (Cl*/(Cl + Cl*)) was measured as a function of the excitation wavelength. The relative Cl* yield reaches a maximum at around λphot = 460 nm. Decomposition of these branching ratios into Cl and Cl* photofragment yield spectra provides insight into the BrCl B-state 3П(0+) non-adiabatic dissociation dynamics. Our results suggest that the dissociation mechanism involves non-adiabatic transitions among 0+ potential energy curves.

AN ELECTRON IMPACT STUDY OF SOME C8HI0 ISOMERS

1965 ◽  
Vol 43 (1) ◽  
pp. 211-218 ◽  
Author(s):  
F. Meyer ◽  
P. Haynes ◽  
Stewart McLean ◽  
A. G. Harrison
Keyword(s):  
Mass Spectrum ◽  
Electron Impact ◽  
Mass Spectra ◽  
Major Part ◽  
The Other ◽  
Fragmentation Pattern ◽  
Impact Study ◽  
Deuterium Labelling ◽  
Appearance Potential ◽  
Alkyl Benzenes

The mass spectra of 1-, 2-, and 6-methylspiro[2.4]hepta-1,3-diene have been measured and found to be very similar to the spectra of 7-methylcycloheptatriene and the isomeric alkyl benzenes. It is concluded that in all cases the major part of the fragmentation occurs by identical paths involving identical intermediates. This conclusion is supported by deuterium labelling and appearance potential data. On the other hand the mass spectrum of 2,5-dimethyl-1,5-hexadien-3-yne, an acyclic C8H10 isomer, shows a number of significant differences in its fragmentation pattern. These differences are reflected in the energetics of ion formation and it is concluded that in this case the fragmentation proceeds through different intermediates.

scholarly journals Fragmentation pattern of amides by EI and HRESI: study of protonation sites using DFT-3LYP data

RSC Advances ◽  
2018 ◽  
Vol 8 (38) ◽  
pp. 21407-21413 ◽  
Author(s):  
H. H. Fokoue ◽  
J. V. Marques ◽  
M. V. Correia ◽  
L. F. Yamaguchi ◽  
X. Qu ◽  
...  
Keyword(s):  
Computational Studies ◽  
Fragmentation Pattern

The N–CO cleavage of α,β-unsaturated piperamides under EI and ESI is supported by computational studies.

scholarly journals Nonlinear Double-arm Optical Tweezers for Controlling 3D Microspheres

2020 ◽  
Vol 30 (4) ◽  
pp. 355
Author(s):  
Nguyen Manh Thang
Keyword(s):  
Optical Tweezers ◽  
Intensity Distribution ◽  
Laser Power ◽  
Laser Intensity ◽  
Optical Trap ◽  
Optical Tweezer ◽  
Organic Dye ◽  
Objective Lens ◽  
Proposed Model ◽  
3D Microspheres

In this paper, a new nonlinear double-arm optical tweezer combining Mach-Zenhder interferometer, objective lens and organic dye layer is proposed. Based on the ray-optical and wave optical approximations, the expression describing the separation of two trap centers and laser intensity distribution is derived. The obtained results show that the separation between two trap centers, the laser intensity distribution, trap region's area and optical trap efficiency can be controlled by tuning laser power. The proposed model is seen to be a double-arm optical tweezer for controlling 3D microsphere by optical method.

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