Ion Branching Ratios Research Articles

Energy distributions of emitted ion fragments following C(1s) excitations in CO.

Ion-branching ratios following the relaxation of C (1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$,nl\ensuremath{\lambda},${\mathit{v}}^{\ensuremath{'}}$) synchrotron light-excited, vibrationally resolved resonances in CO have been measured using a time-of-flight spectrometer at high extraction voltages. Additional measurements at low extraction voltages (higher kinetic-energy resolution) have enabled an estimate of the kinetic-energy distributions (KED's) of the emitted ${\mathrm{C}}^{+}$, ${\mathrm{O}}^{+}$, ${\mathrm{C}}^{2+}$, and ${\mathrm{O}}^{2+}$ ions. Large differences in these distributions are observed at various resonances and, for instance, a doorway-state dependence of the KED has been found for the 3s\ensuremath{\sigma} and 3p\ensuremath{\pi} Rydberg resonances. While the results give some different information concerning the involved relaxation processes, more theoretical calculations are needed to get a more quantitative understanding. \textcopyright{} 1996 The American Physical Society.

Target dependence of multi-electron processes in Iq+ (q=10, 15)+rare gas (Ne, Ar, Kr and Xe) collisions

We have determined experimentally the absolute cross sections for i-electron capture (to projectile) and j-electron removal (from target) ( sigma q,q-ij), total electron capture ( sigma q= Sigma i sigma q,q-i), j-electron removal ( sigma qj= Sigma i sigma q,q-ij) and i-electron capture ( sigma q,q-i= Sigma j sigma q,q-ij) for the processes: Iq+(q=10 or 15)+B to I(q-i)++Bj++(j-i)e (B identical to Ne, Ar, Kr and Xe) at collision energy of 1.5q keV. Charge-state distributions of the scattered ions were measured in coincidence with the recoil ions. The absolute electron-capture cross sections were measured by the initial growth-rate method. The experimental results for sigma q and sigma qj were compared with the predictions of the extended classical over-barrier model (ECBM). The branching ratios of the multiply-excited ions produced by multi-electron transfer have also been determined.

Ion–molecule reactions of ArN+2 with simple aliphatic hydrocarbons at thermal energy

The product ion distributions and rate constants are determined for ion–molecule reactions of ArN+2 with C2Hn (n=2,4,6) and C3Hn (n=6,8) by using a thermal ion–beam apparatus. Although charge-transfer channels leading to parent ions and/or fragment ions are found, no displacement reaction leading to ArCmH+n and N2CmH+n is detected. A comparison of the product ion distributions with breakdown patterns of the parent ions suggests that fragment ions, formed through cleavage of C–H and/or C–C bonds, are produced via near-resonant ionic states in the 13.1–13.4 eV range. The branching ratios of parent ions for C2H4 (68%) and C3H6 (20%) are larger than those for C2H6 (5%) and C3H8 (5%). The large branching ratios of the parent ions for the unsaturated hydrocarbons are explained as due to a strong interaction of a vacant orbital of ArN+2 with the highest occupied πC=C orbital of the unsaturated hydrocarbons which induces nonresonant charge transfer. The total rate constant for C2H2 is 6.8×10−10 cm3 s−1, while those for C2Hn (n=4,6) and C3Hn (n=6,8) are in the range (8.5–9.8)×10−10 cm3 s−1. The former and the latter values correspond to 69% and 77%–90% of the calculated values from Langevin or average dipole orientation (ADO) theory. The smaller kobs/kcalc ratio for C2H2 is attributed to the lack of near-resonant ionic states with favorable Franck–Condon factors for ionization.

Single- and double-photoionization cross sections of carbon dioxide (CO2) and ionic fragmentation of CO2+ and CO22+

Single- and double-photoionization processes of carbon dioxide (${\mathrm{CO}}_{2}$) have been studied in the photon-energy region of 30--100 eV by use of time-of-flight mass spectrometry and the photoion-photoion coincidence method together with synchrotron radiation. The single- and double-photoionization cross sections of ${\mathrm{CO}}_{2}$ are determined. Ion branching ratios and the partial cross sections for the individual ions, respectively produced from the precursors ${\mathrm{CO}}_{2}^{+}$ and ${\mathrm{CO}}_{2}^{2+}$, are determined separately at excitation energies where the molecular and dissociative single- and double-photoionization processes occur simultaneously. The threshold for the molecular double photoionization was found to be 37.6\ifmmode\pm\else\textpm\fi{}0.3 eV. The thresholds for the ${\mathrm{CO}}^{+}$+${\mathrm{O}}^{+}$ and ${\mathrm{C}}^{+}$+${\mathrm{O}}^{+}$ channels of ${\mathrm{CO}}_{2}^{2+}$ are at 39.2\ifmmode\pm\else\textpm\fi{}0.3 and 47.2\ifmmode\pm\else\textpm\fi{}0.5 eV, respectively. Furthermore, in single photoionization, the production of ${\mathrm{CO}}_{2}^{+}$ is dominant, whereas with double photoionization, dissociation becomes dominant.

A note on dissociative photoionization of neopentane in the 10–30 e V photon energy range

Abstract The photofragmentation of neopentane in the photon energy range 10–30 eV with synchrotron radiation is analysed and compared with previous data on mass and photoelectron spectra of this molecule. A broad maximum due to a shape resonance in the ion yield of the most abundant fragment ions is observed around 16 eV photon energy along with Rydberg series converging to the 2a 1 −1 ionization threshold. The analysis of the branching ratios of the main fragment ions hints at a preferential decay of the shape resonance through the ionization channel 3t 2 −1 .

Shake-off processes in photoionization and Auger transition for rare gases irradiated by soft X-rays

Branching ratios of multiply charged Ne, Ar, Kr and Xe ions produced following soft X-ray absorption by the rare gases have been measured using a time-of-flight mass spectrometer and monochromatized synchrotron radiation. Ratios of double, triple and quadruple valence photoionization to single valence photoionization, of multiple Auger transitions to the normal Auger transition from a core hole or core-valence two-hole state, and of the multiple photoionization with a core hole to single core photoionization have been determined using the measured branching ratios of the multiply charged ions.

Single-, double-, and triple-photoionization cross sections of carbon monoxide (CO) and ionic fragmentation of CO+, CO2+, and CO3+

Single-, double-, and triple-photoionization processes of carbon monoxide (CO) have been studied in the photon-energy region of 37--100 eV by use of time-of-flight mass spectrometry and a photoion-photoion-coincidence method together with synchrotron radiation. The single-, double-, and triple-photoionization cross sections of CO are determined. Ion branching ratios and the partial cross sections for the individual ions respectively produced from the precursors ${\mathrm{CO}}^{+}$ and ${\mathrm{CO}}^{2+}$ are determined separately at excitation energies where the molecular and dissociative single- and double-photoionization processes compete. The threshold for the molecular double photoionization was found to be 41.3\ifmmode\pm\else\textpm\fi{}0.2 eV. Furthermore, in single photoionization, the production of ${\mathrm{CO}}^{+}$ is dominant whereas with double photoionization dissociation becomes dominant.

Single- and double-photoionization cross sections of nitric oxide (NO) and ionic fragmentation of NO+ and NO2+

Single- and double-photoionization processes of gaseous nitric oxide (NO) have been studied in the photon energy region 37\char21{}100 eV by use of time-of-flight mass spectrometry and a photoion-photoion-coincidence method together with synchrotron radiation. The single- (${\mathrm{\ensuremath{\sigma}}}^{+}$) and double- (${\mathrm{\ensuremath{\sigma}}}^{2+}$) photoionization cross sections of NO are determined. Dissociation ratios of the precursors ${\mathrm{NO}}^{+}$ and ${\mathrm{NO}}^{2+}$ are determined separately at the excitation energies where the single and double photoionization are in competition. The results show that the metastable ${\mathrm{NO}}^{2+}$ ions amount to about 15% at higher photon energies in the double-photoionization processes. Ionic branching ratios and the partial cross sections for the individual ions produced from the precursors ${\mathrm{NO}}^{+}$ and ${\mathrm{NO}}^{2+}$ are also presented. The threshold for the dissociative double photoionization was found to be 41.0\ifmmode\pm\else\textpm\fi{}0.5 eV.

Single-, double-, and triple-photoionization cross sections of carbonyl sulfide (OCS) and ionic fragmentation of OCS+, OCS2+, and OCS3+

Single-, double-, and triple-photoionization processes of carbonyl sulfide (OCS) have been studied in the photon-energy region of 20\char21{}100 eV by use of time-of-flight mass spectrometry and a photoion-photoion coincidence method together with synchrotron radiation. The single (${\mathrm{\ensuremath{\sigma}}}^{+}$), double (${\mathrm{\ensuremath{\sigma}}}^{2+}$), and triple (${\mathrm{\ensuremath{\sigma}}}^{3+}$) photoionization cross sections of OCS are determined; the double-photoionization cross section is found to be considerably larger at h\ensuremath{\nu}=60 eV, giving a ratio ${\mathrm{\ensuremath{\sigma}}}^{2+}$/${\mathrm{\ensuremath{\sigma}}}^{+}$ of 0.34, than found from previous observations of other molecules (${\mathrm{SO}}_{2}$ and ${\mathrm{CH}}_{4}$). The ratio is in close agreement with that for the isoelectronic zinc atom. Ionic fragmentation ratios of the parent ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions are determined separately at the excitation energies where the single and double photoionization takes place concomitantly. The results show that both the (meta)stable ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions amount to about 10\char21{}15 % at higher photon energies in the respective single- and double-photoionization processes. Ionic branching ratios and the partial cross sections for the individual ions produced from the parent ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions are also presented. High-lying electronic states of the ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ precursors are also observed.

Standard reference spectra for tandem mass spectrometry quality assurance, performance evaluation and proficiency testing: Tandem mass spectrometers which use RF‐only multipole collision cells

AbstractThe collisionally activated dissociation (CAD) of the acetone cation (m/z 58) can be used for quality assurance, performance evaluation, and proficiency testing of CAD measurements in tandem mass specstrometry (MS/MS) instruments which use RF‐only multipole collision cells. The absolute branching ratios (product distributions) of the CAD fragment ions, when measured as a function of the center‐of‐mass collision energy Ecm, can provide an objective basis for quality assurance whenever MS/MS methods are used (viz, to validate how well the target thickness, ion‐containment efficiency, and collision energy are being controlled in various instruments).

Dissociative chemistry of ionic transition metal cluster fragments

The ionic fragments formed by collision-induced dissociation of Mn2(CO) + ions (y=1–10) are reported. The ratio of product ions formed by metal-metal vs. metal-ligand bond cleavage are discussed in terms of the dependence of the metal-metal bond energy on the metal-to-ligand ratio. The collision-induced dissociation data indicate that the metal-metal bond energy of Mn2(CO) 5 + and Mn2(CO) 10 + is less than that for Mn2(CO) + (y=1–4 and 6–9). The product ions arising by metal-metal and metal-ligand bond cleavage reactions for collision-induced dissociation and photodissociation are compared. On the basis of this data and the known photochemistry/photophysics of Mn2(CO)10, it is proposed that the difference in collision-induced dissociation and photodissociation product ion branching ratios is attributable to spin-orbit transitions of the activated ions.

Instrument‐independent database for collisionally activated dissociation in radiofrequency‐only quadrupoles. Single‐collision versus multiple‐collision conditions

AbstractThe collisionally actived dissociation (CAD) of the acetone cation (m/z 58) and of the acetyl cation (m/z 43) from acetone were studied under single‐collision and multiple‐collision conditions. A kinetics‐based measurement protocol developed at the National Institute of Standards and Technology was used to measure the CAD spectra (i.e., the product distributions (branching ratios) of the CAD fragment ions). A protocol is proposed for a second interlaboratory round robin to explore the feasibility (or lack thereof) of measuring standardized, instrument‐independent CAD spectra under multiple‐collision conditions.

Rotationally resolved photoelectron angular distributions in resonance enhanced multiphoton ionization of NO

We report calculated ionic rotational branching ratios and associated photoelectron angular distributions for (1+1′) resonance enhanced multiphoton ionization (REMPI) via the R21(20.5), P21+Q11(25.5), and P11(22.5) branches of the A 2 Σ+(3sσ) state of NO. The branching ratios are dominated by even angular momentum transfer peaks, in agreement with the ΔN+l=odd (ΔN≡N+−Ni ) selection rule. Whereas the calculated photoelectron angular distributions are very branch dependent alignment, the ionic branching ratios are found to be less so. The present calculated results agree well with the experimental results of Allendorf et al.

Dissociative photoionization of N2O: Analytical photoion spectroscopy

Branching ratios of ions produced from the dissociative photoionization of N2O have been measured by using a time-of-flight mass spectrometer and synchrotron radiation in the 15–36 eV region. The branching ratios in the Franck–Condon gap (15.0–16.4 eV) indicate that the autoionizing Rydberg states in this region predissociate to NO+ and O+ through various dissociative states. The results obtained by the analytical photoion spectroscopy above the gap show dissociation pathways of the N2O+ ions. These pathways are discussed by comparing with the reported electronic states of ions and super excited neutrals.

Ionic fragmentation of K-shell excited and ionized CO.

Quantitative ion yields from photoionization of gaseous CO have been measured with time-of-flight mass spectrometry and photoion-photoion coincidence techniques using synchrotron radiation from 270 to 360 eV and from 515 to 615 eV, in the region of C 1s and O 1s excitation and ionization. Dissociative multiple-ionization efficiencies, ion-branching ratios, and the relative yields of all possible ionization reactions are derived. The distributions of kinetic energies released to the (${\mathrm{C}}^{+}$+${\mathrm{O}}^{+}$) and (${\mathrm{C}}^{2+}$+${\mathrm{O}}^{+}$) pairs are measured. Very large contributions of symmetric dissociative double ionization producing ${\mathrm{C}}^{+}$ and ${\mathrm{O}}^{+}$ are found, even in the region of the 1s\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{*}}$ resonances. The results are discussed in the context of the autoionization and Auger electron spectroscopy of core-excited CO and with the aid of recent calculations of the potential curves of ${\mathrm{CO}}^{2+}$. The relationship between the present results and those for photon-stimulated desorption following core excitation and ionization of solid and chemisorbed CO is explored.

A study of the reactions of F + with neutral molecules at room temperature

The thermal energy reactions of the ion F + with O 2, N 2, CO, NO, H 2, CO 2, N 2O, SO 2, OCS, H 2S, NH 3 and CH 4 have been studied at room temperature using a selected ion flow tube apparatus. Reaction rate coefficients and product ion branching ratios have been determined.

Differentiating geometric isomers by laser-ion beam photodissociation

The laser-ion beam photodissociation reactions of the cis-1,3-pentadiene and trans-1,3-pentadiene C/sub 5/H/sub 8//sup +/ ions and the cis,trans-2,4-hexadiene and trans,trans-2,4-hexadiene C/sub 6/H/sub 10//sup +/ ions have been investigated. The photodissociation spectra are found to agree qualitatively with the published ion cyclotron resonance (ICR) photodissociation data. Although the C/sub 5/H/sub 8//sup +/ and C/sub 6/H/sub 10//sup +/ geometric isomers exhibit indistinguishable photodissociation spectra and product ion branching ratios, the wavelength-dependent kinetic energy release values are unique for the individual isomers. The significant changes in the photofragment kinetic energy release values for the trans-1,3-pentadiene and trans,trans-2,4-hexadiene ions as a function of photon energy are attributed to isomerization of the photoexcited parent ion prior to dissociation. 28 references, 5 figures, 2 tables.

A selected ion flow tube study of the reactions of the gaseous ion HCl + at 295 K

Reactions of the gaseous ion HCl + in its ground state were studied at 295 ± 5 K using a selected ion flow tube. Reaction rate coefficients and product ion branching ratios were determined for the reactants H 2, Xe, NO, O 2, CO, CO 2, N 2O, H 2S, COS, SO 2, NH 3 and CH 4. The reaction channels observed were proton or electron transfer, or both, except for H 2 where H-atom transfer was observed.

A selected ion flow tube study of the reactions of the gaseous ion CO +2 at 298 K

The thermal energy reactions of the gaseous ion CO + 2 with the neutral reactants O 2, H 2, CH 4, CH 3Cl, NO, H 2S, COS, SO 2 and NH 3 have been studied at 298 K using a selected ion flow tube (SIFT) apparatus. Reaction rate coefficients and, where appropriate, product ion branching ratios have been determined.

Multiphoton ionization mass spectroscopy of deuterated analogs of acetaldehyde: Evidence for deuterium scrambling

Fragmentation patterns as a function of laser flux are obtained for CD3CHO using a quadrupole mass spectrometer for excitation at the origin of the two-photon resonant n→3s Rydberg transition at 55 138 cm−1. Extensive fragmentation is found with product ion branching ratios showing a strong dependence on laser flux. Fragments such as CDO+ appear, indicating that bond rearrangement occurs. In the case of the CD+3, CD2H+ ion pair, the CD2H+ scrambled product dominates, although in no case does the scrambling reach the statistical limit obtained by assuming that all hydrogen species are equivalent. The individual ion signal data can be fit with a rate equation model. Isotopic selectivity for mixtures of CD3CDO/CH3CHO is demonstrated; no partially deuterated products are found, indicating that the scrambling in CD3CHO is not collisionally induced.