Absolute Branching Ratios Research Articles

Absolute determination of Λ c and D s branching ratios

In this paper we focus on two aspects of charm production in neutrino interactions: low-multiplicity processes such as the diffractive D s and the quasi-elastic charmed-baryon production. We shall show that these processes allow a clear identification of the charmed hadron, and therefore a very good estimate of absolute decay branching ratios. Together with low systematic errors, these measurements can provide, for instance, a precise measurement of f D s .

Infrared laser absorption measurements of HCl( v=1) production in reactions of Cl atoms with isobutane, methanol, acetaldehyde, and toluene at 295 K

Absolute rate coefficients and branching ratios for production of HCl( v=1) are measured for the reactions of Cl with (CH 3) 3CH, CH 3OH, CH 3CHO, and C 6H 5CH 3. The fractions of HCl( v=1) produced ( f=HCl( v=1)/HCl (total)) are f((CH 3) 3CH)=0.03±0.02, f(CH 3OH)=0.12±0.02, f(CH 3CHO)=0.54±0.04, and f(C 6H 5CH 3)=0.47±0.03; a significant fraction of the exothermicity appears in HCl vibration. Rate coefficients at 295 K are k((CH 3) 3CH)=(1.49±0.02)×10 −10, k(CH 3OH)=(5.6±0.2)×10 −11, k(CH 3CHO)=(8.3±0.1)×10 −11, and k( C 6 H 5 CH 3)=(6.1±0.2)×10 −11 cm 3 molecule −1 s −1 .

Prediction of absolute rate coefficients and product branching ratios for the C(3P)+allene reaction system

Complex chemical reactions in the gas phase can be decomposed into a network of elementary (e.g., unimolecular and bimolecular) steps which may involve multiple reactant channels, multiple intermediates, and multiple products. The modeling of such reactions involves describing the molecular species and their transformation by reaction at a detailed level. Here we focus on a detailed modeling of the C(3P)+allene (C3H4) reaction, for which molecular beam experiments and theoretical calculations have previously been performed. In our previous calculations, product branching ratios for a nonrotating isomerizing unimolecular system were predicted. We extend the previous calculations to predict absolute unimolecular rate coefficients and branching ratios using microcanonical variational transition state theory (μ-VTST) with full energy and angular momentum resolution. Our calculation of the initial capture rate is facilitated by systematic ab initio potential energy surface calculations that describe the interaction potential between carbon and allene as a function of the angle of attack. Furthermore, the chemical kinetic scheme is enhanced to explicitly treat the entrance channels in terms of a predicted overall input flux and also to allow for the possibility of redissociation via the entrance channels. Thus, the computation of total bimolecular reaction rates and partial capture rates is now possible.

Dissociative recombination of D+(D2O)2 water cluster ions with free electrons

Dissociative recombination (DR) of the water cluster ion D+(D2O)2 has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Cluster ions were injected into the ring and accelerated to an energy of 2.28 MeV. The stored ion beam was merged with an almost monoenergetic electron beam, and neutral fragments produced by DR were detected by an energy-sensitive surface barrier detector. The first experimental determinations of the absolute DR cross section and branching ratios for a cluster ion are reported. The cross section for the process D+(D2O)2+e− is large and reaches 6⋅10−12 cm2 at a low center-of-mass collision energy of 0.001 eV. The cross section has an E−1.19±0.02 dependence in the energy range 0.001–0.0052 eV, and a steeper slope with an E−1.70±0.12 dependence for E=0.052–0.324 eV. The general trends are similar to the results for previously studied molecular ions, but the cross section is higher in absolute numbers for the cluster ion. Thermal rate coefficients for electron temperatures of 50–2000 K are deduced from the cross section data and the rate coefficients are consequently also large. Branching ratios for the product channels are determined with a grid technique. Break-up into 2D2O+D is the dominating dissociation channel with a probability of 0.94±0.04. The channel resulting in the fragments D2O+OD+D2 has a probability of 0.04±0.02, and the probability for formation of D3O+D2O is 0.02±0.03. The results are compared with data for molecular ions, and the cluster dissociation dynamics are discussed.

Mechanisms and rates of the reactions C 2H 5+O and 1-C 3H 7+O

The mechanisms and rates of the reactions of the primary alkyl radicals ethyl and l-propyl with oxygen atoms at room temperature and low pressure (around 5 mbar) have been studied using two independent experimental arrangements. The reactants were generated by UV-laser flash photolysis with different precursors (C2H5COC2H5, C2H6+CFCl3, C2H5I, C3H7COC3H7, SO2). Stable species concentrations were measured quantitatively by Fourier transform IR and OH radical concentrations of the ground (v=0) and first vibrational (v=1) state by time-resolved laser-induced fluorescence. For both reaction 1 and reaction 2, the mechanism is explained in terms of the formation and subsequent decomposition of a chemically activated alkoxy radical and a competing abstraction channel leading directly to OH and the alkene: C2H5+O→C2H5 (reaction Ia)/C2H5O→HCHO+CH3 (reaction la1)/CH3CHO+H (reaction 1a2)//C2H5+O→C2H4+OH (reaction 1b). The absolute branching ratio was determined preferentially using diethyl ketone as the C2H5 radical source leading to (1a2)/(1a2)/(1b), 32/44/24. Relative branching ratios for the C2H5 radical sources C2H6 +Cl and C2H5I were derived as (1a1/(1a2)=1/1.5 and 1/1.55, respectively. The overall rate coefficient of the reaction C2H5+O was measured as k1=(1.04±0.1)×1014 cm3 mol−1 s−1 and in addition k(C2H5+OH)=(7.0±1)×1013 cm3 mol−1 s−1. The mechanism and the rate of reaction 2 were found as 1-C3H7+O→1-C3H7O (reaction 2a)/1-C3H7O→HCHO+C2H5 (reaction 2a1)/C2H5CHO+H (reaction 2a2)//1.C3H7+O→C3H6+OH (reaction 2b) (branching ratio (2a1)/(2b), 44/32/24 and k2=(8.2±1)×103 mo−1 s−1 The results are discussed in terms of statistical rate theory.

Measuring absolute branching ratios of charmed baryons in B decays

The B factories are expected to provide huge samples of single B decay events with little background by reconstructing one of the B mesons produced in $\Upsilon (4S)$ decays. This represents a new experimental paradigm: such samples will allow to make measurements of a quality previously thought unrealistic. As example we discuss how absolute branching ratios for exclusive as well as inclusive charm baryon decays can be extracted. One starts out by observing decays like $B^- \to \bar p X$ as a signature for $B^- \to \Lambda _c \bar p X$ etc. and then exploits various correlations of the flavour of the B meson with the baryon number of the (anti)proton and other observables like the charge of a lepton, baryon number of another baryon etc. An integrated luminosity of about 500 fb-1 as could be available by 2005 should be sufficient for the task.

Reaction of Carbon Atoms, C (2p2,3P), with Hydrogen Sulfide, H2S (XA1): Overall Rate Constant and Product Channels

The multichannel C + H2S reaction was studied, at room temperature, in a low-pressure fast-flow reactor. Carbon atoms were obtained from the reaction of CBr4 with potassium atoms. The overall rate constant was found to be (2.1 ± 0.5) × 10-10 cm3 molecule-1 s-1, close to the gas kinetic limit. Absolute product branching ratio was estimated over the channels yielding H atoms probed by resonance fluorescence in the vacuum ultraviolet: H + HCS or HSC (75 ± 25)%. Ab initio studies of the different stationary points relevant to this reaction have been performed at the CCSD(T)/cc-pVTZ//QCISD/cc-pVDZ level. In agreement with the measured rate constant, the insertion transition structure leading to triplet HSCH is found lower in energy than the reactants. The reaction is found to proceed via H2SC (3A‘ ‘) intermediate that then rearrange to HSCH. On the basis of RRKM calculations, this last species leads mainly to HCS + H products.

Dissociative recombination of D3O+ and H3O+: Absolute cross sections and branching ratios

Dissociative recombination of the polyatomic ions D3O+ and H3O+ with electrons have been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Absolute cross sections have been determined from 0.001 eV to 0.25 eV center-of-mass energy for D3O+ and from 0.001 eV to 28 eV for H3O+. The cross sections are large (7.3×10−13 cm2 for D3O+ and 3.3×10−12 cm2 for H3O+ at 0.001 eV). At low energies, the cross sections for D3O+ are E−1 energy dependent whereas it is slightly steeper for H3O+. A similar E−1 energy dependence was also observed by Mul et al. [J. Phys. B 16, 3099 (1983)] with a merged electron-ion beam technique for both H3O+ and D3O+ and by Vejby-Christensen et al. [Astrophys. J. 483, 531 (1997)] with the ASTRID storage ring in Denmark, who presented relative cross sections for H3O+. A resonance has been observed around 11 eV for H3O+. It reflects an electron capture to Rydberg states converging to an excited ionic core. A similar structure was reported by Vejby-Christensen et al. Our absolute measurements are in fairly good agreement with those from Mul et al., which were first divided by 2 (Mitchell, 1999, private communication) and from Heppner et al. [Phys. Rev. A 13, 1000 (1976)] for H3O+. Thermal rates were deduced from the measured cross sections for electron temperatures ranging from 50 K to 30 000 K. At 300 K, the thermal rate is equal to 7.6×10−7 cm3 s−1 for H3O+ and to 3.5×10−7 cm3 s−1 for D3O+. Complete branching ratios for all the possible product channels have been determined from 0 eV to 0.005 eV center-of-mass energy for D3O+ and at 0 eV for H3O+, using a well-characterized transmission grid in front of an energy-sensitive surface-barrier detector. No isotope effect was observed within the experimental uncertainties. The three-body break-up channel OX+X+X (where X stands for H or D) is found to occur for 67%–70% of the dissociations. Water or heavy water is produced with an 18%–17% probability and the production of oxygen atoms is negligible. These results support the three-body break-up dominance already found by Vejby-Christensen et al. for the DR of H3O+ in a similar heavy-ion storage ring experiment. However, even if the general trend is the same for both storage rings, significant differences have been observed and will be discussed.

Photodissociating trimethylamine at 193 nm to probe dynamics at a conical intersection and to calibrate detection efficiency of radical products

This paper reports crossed laser-molecular beam scattering experiments measuring the photofragment velocities and product branching in the photodissociation of trimethylamine (N(CH3)3) at 193 nm. We have observed two primary N–CH3 bond fission channels that ultimately produce different nitrogen-containing species, CH3+N(CH3)2 (X̃ 2B1); CH3+N(CH3)2*→CH3+CH2NCH3+H. The data also indicate that a third minor channel may contribute to the dissociation dynamics, CH3+N(CH3)2†→CH3+NC2H4+H2. The experiments show that ground state N(CH3)2 radicals are formed in the photodissociation, in sharp contrast to the exclusive production of NH2 (Ã 2A1) in a similar molecule, methylamine. We discuss how this results from the differing dynamics through the S1–S0 conical intersection in the exit channel in these two dissociating amines. We also use the photodissociation results to calibrate the mass spectrometric sensitivity at the m/e=15 daughter ion for methyl radicals vs N(CH3)2 and CH2NCH3 products. This provides the only necessary calibration to determine an absolute branching ratio in any system producing a methyl radical in one reaction channel and N(CH3)2 (X̃ 2B1) or CH2NCH3 in other reaction channels.

Photoabsorption and photoionization of propyne

This work measured the absolute photoabsorption cross section of propyne (methylacetylene, CH3CCH) in the 6–30 eV energy range. The valence-shell oscillator strength of 16.97 and the static dipole polarizability of 35.82 atomic units (5.31 Å3) were also derived from the photoabsorption spectrum by the sum-rule method. In the photoionization measurement, the first ionization energy 10.369±0.007 eV of propyne and appearance energies for ion fragments were determined. In addition, new vibrational ν9 and ν10 progressions associated with the X 2E ion state of propyne and Rydberg transitions converged to the A 2E ion state were identified. In addition to the main ν3 progression with the vibrational interval of 1979±39 cm−1, the ν9 and ν10 vibrational structures of the X 2E ion state were resolved with vibrational frequencies of 586±74 cm−1 and 289±65 cm−1, respectively. Moreover, the absolute branching ratios, photoionization quantum yield, and partial photoionization cross sections for C3H4+, C3H3+, C3H2+, and C3H+ production in the 10.3–21.4 eV region were determined. Four shape resonance states were tentatively assigned at 11.2, 12.7, 14.8 and 15.8, and 16.7 eV. Furthermore, a CD3CCH isotopic measurement was taken to examine the reaction pathways of H-dissociative photoionization of propyne. According to the evolution of the C3D3+/C3D2H+ ratio, plausible decay mechanisms for H-dissociative photoionization of propyne were proposed.

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The absolute cross section and branching ratios for dissociative recombination of CH -->+2 with electrons have been measured by means of the heavy-ion storage ring CRYRING. Contrary to what has been previously believed, recombination of CH -->+2 is dominated by the three-body channel C + H + H (63%), whereas breakup into the CH + H and C + H2 channels occurs with branching ratios of 25% and 12%, respectively. The thermal rate coefficient for dissociative recombination at 300 K is 6.4 × 10-7 cm3 s-1, which is higher by a factor of 2.5 than the value used in modeling dark molecular clouds. The low CH production and the high production of energetic carbon atoms could be favorable factors for the turbulence model to explain the large abundance of interstellar CH+. The cross section for dissociative excitation was also measured and found to be in good agreement with results from a crossed electron-ion beam experiment.

Decay studies of the neutron-deficient isotopes 114–118Ba

The very neutron-deficient isotopes 114–118Ba were produced in 58Ni induced reactions on 58Ni, 60Ni or 63Cu targets. By on-line mass separation of BaF molecules formed in the separator ion source, exceptionally pure sources of these isotopes were available for spectroscopic studies. The β-decays of 114Ba ( T 1 2 = 0.43 −0.15 +0.30 s ), 115Ba ( T 1 2 = 0.45 ± 0.05 s ), 116Ba ( T 1 2 = 1.3 ± 0.2 s ) and 118Ba ( T 1 2 = 5.2 ± 0.2 s ) were investigated for the first time. 114Ba, 115Ba and 116Ba were identified as β-delayed proton emitters and absolute branching ratios for this decay mode were determined to be 20 ± 10%, >15%, and 3 ± 1%, respectively. In the decay study of 118Ba several γ transitions were identified. New information was also obtained on the β-delayed γ radiation of 117Ba. The spectroscopic data were used to determine the production cross-sections for all these isotopes. Results of our half-life measurements and β-delayed proton studies are confronted with theoretical predictions.

Projectile charge dependence of multi-electron transfer processes in highly charged ion-atom collisions

We have measured the absolute multi-electron transfer cross sections and branching ratios for the decay of multiply excited Rydberg ions in slow Iq+-Xe, Ar (10 ⩽ q ⩽ 20) collisions combining the initial growth rate method with coincidence method. We report the incident ion charge dependence of transfer cross sections and branching ratios.

ARGUS results on charmed hadrons

We report on the measurement of the semileptonic D 0 absolute branching ratios, the measurements of the D s 2 *+ (2573) → D 0 K + decay, and study of the excited charmed baryons Λ c *+ (2593) and Λ c *+ (2625).

Investigating conformation dependence and nonadiabatic effects in the photodissociation of allyl chloride at 193 nm

The experiments presented here investigate the competing photodissociation pathways for allyl chloride upon excitation of the nominally ππ*(C=C) transition at 193 nm. The measured photofragment velocity distributions evidence C–Cl bond fission and HCl elimination. The recoil kinetic energy distribution for the HCl products is bimodal, indicating two primary processes for HCl elimination. The experimental measurements show C–Cl bond fission dominates, giving an absolute branching ratio of HCl:C–Cl=0.12±0.03 when the parent molecule is expanded through a nozzle at 200 °C. The branching ratio depends on the nozzle temperature; at 475 °C, the absolute branching ratio measured is HCl:C–Cl=0.24±0.03. We analyze the experimental results along with supporting ab initio calculations and earlier photodissociation studies of vinyl chloride in order to examine the potential influence of nonadiabaticity along the C–Cl fission reaction coordinate and its dependence on molecular conformation.

Determination of Absolute Product Branching Ratios in Mass Spectrometric Experiments: Detecting Acetyl Radicals at CH2CO+

The paper describes a general method for determining absolute branching ratios in mass spectrometric experiments. The method overcomes the chronic obstacle that the daughter ion fragmentation pattern of radical products is usually unknown. We report the absolute product branching ratio for competing primary C−Cl and C−C bond fission in chloroacetone after excitation on the 1nπ* absorption band. To determine this branching ratio, acetyl chloride is used to calibrate the relative detection efficiency of acetyl radicals at the CH2CO+ daughter ion relative to Cl atoms at 35Cl+. We also calculate the daughter ion production probability for CH2CO+ formed from internally excited CH3CO radicals.

Script l]-forbidden Gamow-Teller beta decay of 57Cu.

Absolute branching ratios for the {beta} decay of {sup 57}Cu to excited states up to 3.3 MeV in {sup 57}Ni have been determined, including the l-forbidden Gamow-Teller transition to the first excited state in {sup 57}Ni. Four transitions to excited states at 0.768, 1.113, 2.443, and 3.007 MeV are observed in addition to the superallowed decay to the ground state of {sup 57}Ni. The measured branching ratio to the ground state is 89.9 {plus_minus} 0.8{percent} and the branching ratios to the four excited states are 0.94 {plus_minus} 0.09{percent}, 8.6 {plus_minus} 0.6{percent}, 0.17 {plus_minus} 0.03{percent}, and 0.35 {plus_minus} 0.04{percent}, respectively. In addition we have measured the {sup 57}Cu half-life and find it to be 196.3 {plus_minus} 0.7 ms, which is in good agreement with the most recent measurement. {ital B}(GT) values have been extracted from the new results and are compared to shell model calculations. {copyright} {ital 1996 The American Physical Society.}

Absolute Rate Constant and Product Branching Ratios for the Reaction between H and C2H3 at T = 213 and 298 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAbsolute Rate Constant and Product Branching Ratios for the Reaction between H and C2H3 at T = 213 and 298 KP. S. Monks, F. L. Nesbitt, W. A. Payne, M. Scanlon, L. J. Stief, and D. E. ShallcrossCite this: J. Phys. Chem. 1995, 99, 47, 17151–17159Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100047a018RIGHTS & PERMISSIONSArticle Views137Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

The chemiluminescent studies of the orbital aligned Ca(1P1) with CH4−nCln (n = 1, 2, 3, 4) reactions

The reactions of atomic p orbital aligned Ca(1P1) with CH4−nCln (n = 1, 2, 3, 4) have been studied by means of laser-induced chemiluminescence in a beam-gas apparatus. The reaction of Ca(1P1) + CH3Cl shows a strong preference for perpendicular p orbital approach to CaCl(A2Π) chemiluminescence product channel. Reactions become less sensitive to Ca(1P1) atomic orbital alignment with increasing n. Results are interpreted in terms of the electron-jump model and the orbital-following model. Absolute chemiluminescence cross-sections and branching ratios are also obtained.

Measurement of the absolute branching fractions for D0 decays into [formula omitted

Using the ARGUS detector at the e + e − storage ring DORIS II we have measured the absolute branching ratios of the D 0 meson, Br( D 0→ K − π +)=(3.41±0.12±0.28)%, Br( D 0→ K − π + π + π −)=(6.80± 0.27±0.57)%, and Br(D 0→ K 0 π + π −)=(5.03±0.39±0.49)% .