Absolute photoionization cross-section of the methyl radical

Craig A. Taatjes, David L. Osborn, Talitha M. Selby, Giovanni Meloni, Haiyan Fan, Stephen T. Pratt

Research output: Contribution to journalArticle

72 Citations (Scopus)

Abstract

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; σCH3(10.2 eV) = (5.7 ± 0.9) × 10-18 cm2 and σCH3(11.0 eV) = (6.0 ±2.0) × 10-18 cm2. The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 ± 2.0) × 10-18 cm2 at 10.460 eV, (5.5 ± 2.0) × 10-18 cm2 at 10.466 eV, and (4.9 ± 2.0) × 10-18 cm2 at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

Original languageEnglish
Pages (from-to)9336-9343
Number of pages8
JournalJournal of Physical Chemistry A
Volume112
Issue number39
DOIs
Publication statusPublished - Oct 2 2008
Externally publishedYes

Fingerprint

Photoionization
photoionization
cross sections
Photolysis
photolysis
ketones
Mass spectrometry
mass spectroscopy
Acetone
Synchrotrons
acetone
synchrotrons
vinyl radical
methyl radical
Molecular beams
Pulsed lasers
Iodine
iodides
molecular beams
iodine

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Taatjes, C. A., Osborn, D. L., Selby, T. M., Meloni, G., Fan, H., & Pratt, S. T. (2008). Absolute photoionization cross-section of the methyl radical. Journal of Physical Chemistry A, 112(39), 9336-9343. https://doi.org/10.1021/jp8022937

Absolute photoionization cross-section of the methyl radical. / Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Meloni, Giovanni; Fan, Haiyan; Pratt, Stephen T.

In: Journal of Physical Chemistry A, Vol. 112, No. 39, 02.10.2008, p. 9336-9343.

Research output: Contribution to journalArticle

Taatjes, CA, Osborn, DL, Selby, TM, Meloni, G, Fan, H & Pratt, ST 2008, 'Absolute photoionization cross-section of the methyl radical', Journal of Physical Chemistry A, vol. 112, no. 39, pp. 9336-9343. https://doi.org/10.1021/jp8022937
Taatjes, Craig A. ; Osborn, David L. ; Selby, Talitha M. ; Meloni, Giovanni ; Fan, Haiyan ; Pratt, Stephen T. / Absolute photoionization cross-section of the methyl radical. In: Journal of Physical Chemistry A. 2008 ; Vol. 112, No. 39. pp. 9336-9343.
@article{469b0a2e57c9483fb0cb1a110e34fc3f,
title = "Absolute photoionization cross-section of the methyl radical",
abstract = "The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; σCH3(10.2 eV) = (5.7 ± 0.9) × 10-18 cm2 and σCH3(11.0 eV) = (6.0 ±2.0) × 10-18 cm2. The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 ± 2.0) × 10-18 cm2 at 10.460 eV, (5.5 ± 2.0) × 10-18 cm2 at 10.466 eV, and (4.9 ± 2.0) × 10-18 cm2 at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.",
author = "Taatjes, {Craig A.} and Osborn, {David L.} and Selby, {Talitha M.} and Giovanni Meloni and Haiyan Fan and Pratt, {Stephen T.}",
year = "2008",
month = "10",
day = "2",
doi = "10.1021/jp8022937",
language = "English",
volume = "112",
pages = "9336--9343",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "39",

}

TY - JOUR

T1 - Absolute photoionization cross-section of the methyl radical

AU - Taatjes, Craig A.

AU - Osborn, David L.

AU - Selby, Talitha M.

AU - Meloni, Giovanni

AU - Fan, Haiyan

AU - Pratt, Stephen T.

PY - 2008/10/2

Y1 - 2008/10/2

N2 - The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; σCH3(10.2 eV) = (5.7 ± 0.9) × 10-18 cm2 and σCH3(11.0 eV) = (6.0 ±2.0) × 10-18 cm2. The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 ± 2.0) × 10-18 cm2 at 10.460 eV, (5.5 ± 2.0) × 10-18 cm2 at 10.466 eV, and (4.9 ± 2.0) × 10-18 cm2 at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

AB - The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; σCH3(10.2 eV) = (5.7 ± 0.9) × 10-18 cm2 and σCH3(11.0 eV) = (6.0 ±2.0) × 10-18 cm2. The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 ± 2.0) × 10-18 cm2 at 10.460 eV, (5.5 ± 2.0) × 10-18 cm2 at 10.466 eV, and (4.9 ± 2.0) × 10-18 cm2 at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

UR - http://www.scopus.com/inward/record.url?scp=54249131755&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=54249131755&partnerID=8YFLogxK

U2 - 10.1021/jp8022937

DO - 10.1021/jp8022937

M3 - Article

VL - 112

SP - 9336

EP - 9343

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 39

ER -