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Yu Y, Jiang J, Hua L, Li X, Li H. Pressure-Driven Switching of Photoelectron Impact Ionization-Chemical Ionization/Penning Ionization in Vacuum Ultraviolet Photoionization Mass Spectrometry. Anal Chem 2024; 96:5686-5693. [PMID: 38551337 DOI: 10.1021/acs.analchem.4c00686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/10/2024]
Abstract
Vacuum ultraviolet photoionization (VUV-PI) is a soft ionization technique that operates under pressures ranging from vacuum to ambient pressure. VUV-PI has played an essential role in direct sampling mass spectrometry. In this study, new ionization processes initiated by photoelectrons have been studied through the inclusion of a radio frequency (RF) electric field at different pressures. After deducting the contribution of single photoionization (SPI), the signal intensity of 1 ppmv toluene (C7H8+) in Ar was approximately 5-fold higher than that in N2. Mixed gases with different ionization energies (IEs) and excitation energies (EEs) were further investigated to reveal that metastable species were involved in the enhancement process. Reactant ions were produced by photoelectron impact ionization (PEI), which further triggered ion-molecule reactions, i.e., chemical ionization (CI). Metastable species were produced by photoelectron impact excitation (PEE), which further triggered Penning ionization (PenI). Analytes with IEs above 10.6 eV, such as CO2 (IE = 13.78 eV) and CHCl3 (IE = 11.37 eV), could be sensitively ionized by PenI with a sensitivity comparable to SPI. Except for the contribution of SPI, the dominant ionization process was switched from PEI-CI to PenI when the pressure was elevated from 50 to 500 Pa, as the electron energy gradually decreased and was only able to produce metastable states based on the kinetic energy balance equation of electrons. The conversion processes and conditions from PEI-CI to PenI will provide novel insights to develop new selective and sensitive VUV-PI sources and understand the ionization mechanism in other discharge ionization sources.
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Affiliation(s)
- Yi Yu
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China
- University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Liaoning Key Laboratory for Mass Spectrometry Technology and Instrumentation, Dalian 116023, People's Republic of China
- Dalian Key Laboratory for Online Analytical Instrumentation, Dalian 116023, People's Republic of China
| | - Jichun Jiang
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China
- Liaoning Key Laboratory for Mass Spectrometry Technology and Instrumentation, Dalian 116023, People's Republic of China
- Dalian Key Laboratory for Online Analytical Instrumentation, Dalian 116023, People's Republic of China
| | - Lei Hua
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China
- Liaoning Key Laboratory for Mass Spectrometry Technology and Instrumentation, Dalian 116023, People's Republic of China
- Dalian Key Laboratory for Online Analytical Instrumentation, Dalian 116023, People's Republic of China
| | - Xinyang Li
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China
- Liaoning Key Laboratory for Mass Spectrometry Technology and Instrumentation, Dalian 116023, People's Republic of China
- Dalian Key Laboratory for Online Analytical Instrumentation, Dalian 116023, People's Republic of China
| | - Haiyang Li
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China
- Liaoning Key Laboratory for Mass Spectrometry Technology and Instrumentation, Dalian 116023, People's Republic of China
- Dalian Key Laboratory for Online Analytical Instrumentation, Dalian 116023, People's Republic of China
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Kroner SM, Dematteo MP, Hadad CM, Carpenter BK. The Gas-Phase Acidity of 2(3H)-Oxepinone: A Step toward an Experimental Heat of Formation for the 2-Oxepinoxy Radical. J Am Chem Soc 2005; 127:7466-73. [PMID: 15898796 DOI: 10.1021/ja050173u] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In an effort to gain further insight into the oxidation of the phenyl radical, this contribution details the first of three experiments designed to establish the heat of formation of the 2-oxepinoxy radical. We report here the synthesis of the previously unknown 2(7H)-oxepinone (12a) and 2(3H)-oxepinone (12b). We have determined the gas-phase acidity (Delta(acid)H(298)) of 12b by means of a bracketing study employing a flowing afterglow apparatus with quadrupole mass spectrometric detection. In this experiment, compound 12b was reacted in the gas phase with a series of bases of varying strength. A proton-transfer reaction was observed when 12b was reacted with t-BuS(-), but not when 12b was reacted with HS(-). We conclude that the gas-phase acidity of 12b lies between those of t-BuSH and H(2)S, and it is thereby assigned a value of Delta(acid)H(298) = 352 +/- 2 kcal/mol. Additional support for this value was found by performing the reverse reactions (i.e. the 2-oxepinoxy anion (15a) was reacted with proton sources of differing acidities). Anion 15a underwent a proton-transfer reaction with H(2)S but not with t-BuSH, in agreement with the results from the forward reactions. The experimental value of the gas-phase acidity agrees well with those from DFT calculations, which predicted Delta(acid)H(298) = 348.9 kcal/mol at the B3LYP/6-31+G(d) level and 349.2 kcal/mol at the B3LYP/aug-cc-pVTZ level.
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Affiliation(s)
- Steven M Kroner
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
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Davico GE. The Conversion of Methane to Methanol: A Reaction Catalyzed by I+ or I2+? J Phys Chem A 2005; 109:3433-7. [PMID: 16833680 DOI: 10.1021/jp050046k] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The gas-phase reactions of I+ and I2(+) with methane were studied to determine which species is involved in the oxidation of methane to methyl sulfate, an intermediate in the production of methanol. We found that while I+ reacts readily with methane, I2(+) does not react in our experimental reaction conditions. Reaction products and rate constants are measured and reported. In addition, ab initio calculations were carried out to further understand the reaction mechanism. A revised mechanism of catalysis is proposed which is in excellent agreement with available experimental data and our theoretical computations.
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Affiliation(s)
- Gustavo E Davico
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, USA.
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Nimlos MR, Davico G, Geise CM, Wenthold PG, Lineberger WC, Blanksby SJ, Hadad CM, Petersson GA, Ellison GB. Photoelectron spectroscopy of HCCN− and HCNC− reveals the quasilinear triplet carbenes, HCCN and HCNC. J Chem Phys 2002. [DOI: 10.1063/1.1496473] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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