Low-energy Electron-impact Ionization Research Articles

The detection of CH 3CO, C 2H 5, and CH 3CHO by rempi/mass spectrometry and the application to the study of the reactions H+CH 3CO and O+CH 3CO

The discharge flow reactor technique combined with molecular beam sampling and either resonance enhanced multi-photon ionization (REMPI)/mass spectrometry or low energy electron impact ionization (EI)/mass spectrometry has been used to study the specific and sensitive detection of radicals and molecules and the reaction of radicals with atoms. The acetyl radical CH 3 CO shows a REMPI mass spectrum at m/e =43 in the wavelength region 395–415 nm and at 430 nm. The ethyl radical C 2 H 5 is detected by multi-photon ionization at the wavelength 400–460 nm by the parent ion m/e =29. Acetyldehyde is monitored sensitively by a (2+1) Rydberg transition at 440.6 nm with ion fragmentation at m/e =15, 29, 43. The reaction mechanism of CH 3 CO radicals with H atoms at low pressure (0.01–0.1; 0.5–10 mbar) and temperature (293–300 K) is given by CH 3 CO+H→CH 3 +HCO (7a) →CH 3 CHO (7b) →CH 2 CO+H 2 (7c) Reaction channel (a) is the main route at low pressure (1 mbar) and the ratio of (a)/(b) is discussed in a model of chemical activation/collision stabilization. The rate constant k 1 was determined relative to the reaction C 2 H 5 +H leading to k 7 =(3.3+2)·10 13 cm 3 /mol· s The ratio of the rate constants of acetyl CD 3 CO and vinoxy CD 2 CHO radicals with D atoms was determined as k 7 dd (CD 3 CO+D)/ k 11− d (CD 2 CHO+D)=1.6+0.6 For the reaction CH 3 CO+O→CH 3 +CO 2 (12a) →OH+CH 2 CO (12b) the route (12a) dominates. The rate of this reaction (12) was measured using the reaction C 2 H 5 +O as a standard: k 12 =(1.2±0.4)·10 14 cm 3 /mol· s

A molecular beam time-of-flight mass spectrometer using low-energy-electron impact ionization

We have constructed a versatile apparatus to study photoinitiated processes in molecular beams using a variety of generally applicable techniques. The instrument contains a pulsed, low-energy electron gun that delivers space-charge-limited electron beams into the ionization region of a time-of-flight mass spectrometer. The electron energy is tunable from 8 to 200 eV, and the electron energy distribution is relatively narrow (FWHM ∼0.3 eV), which allows us to ionize laser-excited species and their decomposition products selectively. We have used low-energy electron impact ionization and mass spectrometry to characterize molecular beams, to detect vibrationally excited molecules prepared by vibrational overtone excitation, and to detect primary photodissociation products in the presence of precursor molecules.

A study of the symmetric charge transfer reaction H+2+H2 using the high resolution photoionization and crossed ion–neutral beam methods

A new ion–molecule reaction apparatus, which combines the crossed ion–neutral beam method, high resolution photoionization mass spectrometry, and charge transfer detection, has been developed. Using this apparatus, we have examined the relative total charge transfer cross sections of H+2+H2 as a function of the vibrational state of H+2, v′0 =0–4, at the center-of-mass collision energy (Ec.m.) range of 0.38–200 eV. The relative total charge transfer cross sections measured at Ec.m. =8, 16, 22.5, and 200 eV are in general agreement with a recent theoretical calculation based on the semiclassical energy conserving trajectory formulation. The vibrational energy effects on the cross sections for the charge transfer and the H+3+H channels at low collision energies (Ec.m. ≤1 eV) were directly observed. The rotational states, J=0, 1, and 2, of H+2(v0=0) were also selected in this experiment. Within experimental uncertainties, the rotational excitations of H+2(v′0 =0) have no effect on the relative total charge transfer cross sections at Ec.m. =2 and 4 eV. By calibrating the nominal relative total charge transfer cross sections obtained with an ionizing photon energy of 18 eV (688 Å) to absolute total charge transfer cross sections determined previously using low energy electron impact ionization, absolute total charge transfer cross sections for v0 =0 and 1 in the kinetic energy range of Ec.m. =8–200 eV were estimated. The absolute total charge transfer cross sections thus obtained for v′0=0 and 1 are lower than the theoretical values by approximately a factor of 2. However, the kinetic energy dependence of the total charge transfer cross section is in agreement with the theoretical calculation. The final vibrational state distributions of the charge transfer products H+2 from the reaction H+2(v0=0) +H2(v″0=0) → H2(v′)+H+2(v″) at Ec.m. =4, 8, and 16 eV have been probed by charge transfer reactions H+2(v″)+N2 and H+2(v″)+CO. The results are consistent with the theoretical prediction that approximately 92% and 85% of the product H+2 ions formed at Ec.m. =8 and 16 eV are in the v″=0 state, respectively.

Mass spectrometry at low electron beam energies: A sensitive probe of vibrational excitation

It is shown that the fragmentation pattern of n-C 8H + 18 produced by low-energy electron impact ionization in a modulated beam mass spectrometer is a sensitive function of the initial gas temperature. Under these conditions, mass spectrometry lends itself quite generally to the study of energy deposition and exchange in processes involving polyatomics.

Low energy electron impact attachment and ionization in HgBr2

Cross sections for low energy electron impact attachment and ionization in mercuric bromide (HgBr2) have been measured using an electron beam experiment. The ion products of these reactions, as identified by mass analysis, are Br− and chiefly HgBr+2. Rate coefficients computed from the measured cross sections were found to be in good agreement with values determined independently from an electron swarm experiment.

Measurements of the triple-differential cross section for low-energy electron-impact ionization of argon

The triple-differential cross section for electron-impact ionization of argon has been investigated for the primary electron energies near 100 eV and scattering angle 15\ifmmode^\circ\else\textdegree\fi{}. The in-plane and out-of-plane measurements show that the forward lobe has a true minimum in the full three-dimensional sense when the ejected electron energy is 5 eV. However, such a minimum is not observed when the ejected electron energy is 20 eV. The cross section has much more structure than that of helium. No simple symmetry has been found common to all the cases for argon.

Measurements of the triple-differential cross section for low-energy electron-impact ionization of helium

The triple-differential cross section for ionization of helium by low-energy electron impact is investigated over the energy and angular variables. Measurements have been made for primary electron energies near 100 eV, ejected electron energies of 5, 10, and 20 eV, and scattering angles 15\ifmmode^\circ\else\textdegree\fi{}, 20\ifmmode^\circ\else\textdegree\fi{}, and 30\ifmmode^\circ\else\textdegree\fi{}. The forward lobe of the triple-differential cross section is found to be approximately cylindrically symmetric.

Triple-differential three-dimensional cross sections for low-energy electron impact ionization of helium

Measurements are reported of the triple-differential cross sections for ionization of helium by electron impact. Experimental conditions were chosen to help clarify the situation in the theory of ionization. Data are presented for primary energies of 100, 105, 125 and 165 eV. Unlike previous measurements in this energy regime, data are included for the circumstance where the three electron trajectories are not in a plane.

ChemInform Abstract: THE METHANIUM ION, CH5(+), EVIDENCE FOR THE STRUCTURE OF A NONCLASSICAL ION FROM REACTION STUDIES BY ION CYCLOTRON RESONANCE SPECTROSCOPY

Chemischer InformationsdienstVolume 6, Issue 7 Preparative Organic Chemistry ChemInform Abstract: THE METHANIUM ION, CH5(+), EVIDENCE FOR THE STRUCTURE OF A NONCLASSICAL ION FROM REACTION STUDIES BY ION CYCLOTRON RESONANCE SPECTROSCOPY MICHAEL D. SEFCIK, MICHAEL D. SEFCIKSearch for more papers by this authorJAY M. S. HENIS, JAY M. S. HENISSearch for more papers by this authorPETER P. GASPAR, PETER P. GASPARSearch for more papers by this author MICHAEL D. SEFCIK, MICHAEL D. SEFCIKSearch for more papers by this authorJAY M. S. HENIS, JAY M. S. HENISSearch for more papers by this authorPETER P. GASPAR, PETER P. GASPARSearch for more papers by this author First published: February 18, 1975 https://doi.org/10.1002/chin.197507139AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue7February 18, 1975 RelatedInformation

The methanium ion, CH5+. Evidence for the structure of a nonclassical ion from reaction studies by ion cyclotron resonance spectroscopy

Studies of proton and deuteron transfer from methanium ions to various substrates and collision-induced dissociation of isotopically substituted methanium ions suggest that under the low-energy conditions of the ICR experiment, the addition of a hydrogen ion to methane produces a methanium ion whose hydrogens are structurally and chemically distinguishable. The reactions of methanium ions formed in the low energy electron impact ionization of CH4–CD4 mixtures are compatible with a methanium ion of Cs symmetry in which intramolecular rearrangement does not occur. Reaction studies on the methanium ions formed by the exoergic proton transfer from D3+ to methane indicate that rapid intramolecular rearrangements occur in these ions.

Quantitative protein sequencing using mass spectrometry: Use of low lonizing voltages in mass spectral analysis of methyl- and phenylthiohydantoin amino acid derivatives

The mass spectra of eighteen methylthiohydantoin and thirteen phenylthiohydantoin amino acid derivatives have been recorded at electron energies of 11, 20, and 70 electron volts. It is observed that the spectra of the majority of the derivatives studied were considerably reduced in complexity, containing in some cases only the molecular ion. In all the cases with three exceptions, the molecular ion was the base peak of the low-voltage spectrum. The loss of sensitivity at lower ionizing voltages was measured for a number of compounds and the sensitivity as measured by ion abundance was observed to be at a maximum around 20 eV and to decrease rapidly at lower energies. The use of low-energy electron impact ionization is compared to chemical ionization and the advantages and disadvantages discussed.

Alignment of Ionic Ground State of Xe by Electron-Impact Ionization Observed through Exchange Collision with the Neutral Metastable State

The radio-frequency paramagnetic-resonance method was used to observe the exchange collisions between the singly ionized Xe ground state $^{2}P_{\frac{3}{2}}$ and the neutral metastable state $^{3}P_{2}$. The ionic ground-state and metastable-state atoms are both formed and aligned by unidirectional low-energy high-flux electron-beam impact. The magnetic resonances of even and odd ionic ground-state atoms were observed by monitoring changes in the transparency of the resonance radiation absorbed by the metastable-state atoms. Phenomenological theories are presented which explain the sign of the magnetic-resonance signal of the ionic ground state relative to that of the neutral metastable state, together with independent experimental evidence to support the theories. Conclusive experimental evidence is presented supporting our original assumptions that the ionic ground-state ${\mathrm{Xe}}^{+}(^{2}P_{\frac{3}{2}})$ is aligned by low-energy electron-impact ionization and that such alignment is detectable through the results of exchange collisions with the metastable state.