Design of a high-resolution mass spectrometer for studying the photodissociation of organic ions in the gas phase

1981 ◽  
Vol 374 (1759) ◽  
pp. 461-473 ◽  
Keyword(s):  
Mass Spectrometer ◽  
Ion Source ◽  
Operating Conditions ◽  
Electron Multiplier ◽  
Electric Sector ◽  
Positive Ions ◽  
Free Region ◽  
Field Free Region ◽  
Ion Laser ◽  
Double Focusing

The design and operating conditions of an apparatus to study photodissociation of ions is described. Ions in a large, double-focusing, mass spectrometer are irradiated with photons from an argon-ion laser. A path length of 706 mm for interaction between the ion and laser beams is obtained by passing the radiation through the ion source and then along the same path as that followed by the ions in the first field-free region of the mass spectrometer. By scanning the voltage of the electric sector, different fragment ions resulting from photodissociation are transmitted in turn to an electron multiplier. They are distinguished from ions resulting from unimolecular dissociation by mechanically chopping the laser beam and using the technique of phase-sensitive detection. The photodissociations of the molecular, positive ions of the three isomers of nitrotoluene have been investigated. It is found that, after excitation of the ions with 2.541 eV photons, the resulting fragmentation pathways are different from those for the corresponding unimolecular dissociations.

New methods of identifying organic compounds

1979 ◽  
Vol 293 (1400) ◽  
pp. 157-166 ◽  
Keyword(s):  
Organic Molecules ◽  
Ion Beam ◽  
Structural Features ◽  
Ion Source ◽  
Side Chain ◽  
Fragmentation Pattern ◽  
Electric Sector ◽  
Ion Structure ◽  
New Methods ◽  
Free Region

A 'reversed' geometry mass spectrometer, in which the ion beam passes through the magnetic sector before the electric sector, offers several advantages for the study of large organic molecules. The method used is to select individual ionic species formed in the ion source in turn by using the magnet and to study the fragmentation of these species in the field-free region in front of the electric sector. Either unimolecular or collision-induced fragmentations can be investigated, the masses of the daughter species being determined by scanning the electric sector. By selecting a variety of individual ions, a comprehensive fragmentation ‘ map' of the molecular species can be constructed. Because it is a voltage that is scanned, the instrument can readily be computer controlled which gives improved reproducibility of scanning, together with other advantages. The several pathways that often link a particular fragment ion with the molecular ion provide complementary information concerning ion structure. The fragmentation pattern of any ion is often sufficiently characteristic of the ion structure to allow direct identification of structural features present to be made by comparing the pattern from the relevant ion with that of an ion formed from a known reference compound. By using these methods the molecular structure of large organic molecules can often be deduced. Large isomeric molecules such as steroids, differing only in the structure of a side chain, can be distinguished by selecting only ions containing the side chain for study. The new methods also offer advantages for the detection and identification of individual components in mixtures.

The ionization of fast neutrals by electron impact in the second field-free region of a mass spectrometer of reversed geometry

1988 ◽  
Vol 23 (6) ◽  
pp. 495-498 ◽  
Author(s):  
M. C. Blanchette ◽  
J. L. Holmes ◽  
C. E. C. A. Hop ◽  
A. A. Mommers
Keyword(s):  
Electron Impact ◽  
Mass Spectrometer ◽  
Free Region ◽  
Field Free Region

DEVELOPMENT OF A NOVEL DUAL TIME-OF-FLIGHT IMAGING MASS SPECTROMETER: PRINCIPAL, REALIZATION, AND OPTIMAL PERFORMANCE

2008 ◽  
Vol 15 (04) ◽  
pp. 369-389 ◽  
Author(s):  
I. G. SHUTTLEWORTH
Keyword(s):  
Three Dimensional ◽  
Time Of Flight ◽  
Operating Conditions ◽  
Two Dimensional ◽  
Gas Phase Reactions ◽  
Free Region ◽  
Field Free Region ◽  
Velocity Images ◽  
Working Parameters ◽  
Time Of Flight Imaging

A novel dual time-of-flight imaging analyzer has been developed for studies of gas phase reactions and the scattering or desorption of ions and molecules from surfaces. The analyzer is capable of experimentally selecting a two-dimensional slice of particles from a three-dimensional flux without the necessity for deconvolution of the resulting velocity images by the Abel transform. The analyzer operates through ionization of the scattered species and their subsequent flight through a field-free region. This initial flight allows a dispersion according to the species natural velocity distribution. The second time of flight deflects the ions through a right angle and through a flight tube allowing dispersion according to mass or charge before detection. The analyzer offers two modes of operation — the first of these produces a mass spectrum of the desorbing species, the second produces a two-dimensional velocity map of the desorbing species. Trial results using an effusive beam source and acetone as a test gas have demonstrated the operation of the analyzer. The operation of the analyzer has been simulated and optimized to reduce ion flight aberrations. A set of orthogonal two-dimensional polynomial functions have been derived to reduce residual aberrations across a broad range of operating conditions. An upper limit to the temporal resolution of the analyzer has been established and a set of working parameters for low distortion electron beam ionization have been presented.

Carbon and hydrogen scrambling in the ions C(9+n)H(9+2n)+. Rearrangements of cyclooctatetraene derivatives

1972 ◽  
Vol 25 (5) ◽  
pp. 1107 ◽  
Author(s):  
JH Bowie ◽  
GE Gream ◽  
M Mular
Keyword(s):  
Mass Spectrometer ◽  
Side Chain ◽  
Free Region ◽  
Field Free Region ◽  
Hydrogen Rearrangement ◽  
Hydrogen Scrambling

Carbon and hydrogen scrambling occurs either prior to, or during, the decompositions of the ions C9H9+, CllH13+, and C12H15+ in the first field-free region of the mass spectrometer. The ions may be produced from various substrates, and the decompositions of CllH13+ may be interpreted in terms of a decomposing ion in which some, but not all, of the C-H bonds have broken and reformed. The ions C9H9+ and C10H11+ may be produced by complex hydrogen rearrangement in the side-chain of particular bromo-and hydroxy-alkylcyclooctatetraene derivatives.

Etude par activation collisionnelle des ions [C4H7O]+ provenant des ions penténols et méthylcetones [C5H10O]•+ métastables

1984 ◽  
Vol 62 (9) ◽  
pp. 1740-1746 ◽  
Author(s):  
G. Bouchoux ◽  
Y. Hoppilliard ◽  
R. Flammang ◽  
A. Maquestiau ◽  
P. Meyrant
Keyword(s):  
Mass Spectrometer ◽  
Collisional Activation ◽  
Molecular Ions ◽  
Side Chain ◽  
Molecular Ion ◽  
Free Region ◽  
Field Free Region

The [C4H7O]+ ions arising from 2-pentanone (1), 3-methylbutanone (2), 2-methylbut-3-en-2-ol (3), pent-3-en-2-ol (4), and 3-methylbut-3-en-2-ol (5) by methyl loss were studied by collisional activation. A triple sector (E/B/E) mass spectrometer was used to distinguish between fragment ion structures produced in the source and in the first field free region. The collision induced dissociations confirm or demonstrate that: (i) in the source, the methyl originally on the position 1 in compounds 1–5 is lost to give, respectively, [n-C3H7CO]+ (a), [i-C3H7CO] + (b), [CH3COHCHCH2] + (c), [CH3CHCHCHOH]+ (d), and [CH2C(CH3)CHOH]+ (e), while the methyl loss from the side chain gives, competitively, ion c for the five precursors; (ii) in the first field free region molecular ions 1,3,4, and 5 produce an identical mixture of structures a, b, and c; the molecular ion 2 leads essentially to acylium ion b. The mechanisms and the thermochemistry of the isomerization path of 1–5 are discussed.

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