eV Collision Energy Research Articles

Possible resonance scattering window for CO symmetric charge transfer

Comparison of scattering contour diagrams of CO +/CO symmetric charge transfer generated in low-energy crossed-beam experiments shows anomalous results at 1.1 eV collision energy as compared to results at 0.8 and 2.3 eV collision energy. Similarity with Ar +/N 2 at 0.9±0.15 eV and Ar +/O 2 near 0.85 eV may indicate a quantum-mechanical scattering resonance for CO +/CO near 1 eV was postulated for these previous two systems.

Laser induced crossed-beam charge transfer: Collision energy effects of the Na(3 2P3/2,1/2)+I2→Na++I−2 system

A crossed-beam charge transfer study was carried out for the Na(3 2P3/2,1/2)+I2→Na++I−2 system using laser excitation of the Na atom into its two spin–orbit states. The collision energy effects including the energy threshold and post-threshold laws were measured for both spin–orbit states.

Investigation of collisional‐activation decomposition process and spectra in the transport regions of an electrospray single‐quadrupole mass spectrometer

The use of collisional-activation dissociation (CAD) in the electrospray transport region was evaluated for generating structural information on several pesticides and antibiotics. The collision energy used to generate the CAD spectra could be varied easily by changing the capillary/skimmer potential difference, imparting from 0 eV to above 16 eV internal energy to the near thermal ions generated by electrospray. The internal energy distribution for low-energy collisions (capillary/skimmer potential difference of 20 V) closely matches the curves generated by a triple-quadrupole mass spectrometer. Furthermore, the CAD spectra for selected compounds generated by electrospray in the transport region at a capillary/skimmer potential difference of 30-50 V closely resembled those obtained from the [M + H]+ ion by a triple quadrupole using 30 eV collision energy. The CAD of ions in the transport region resulted in 70% to 80% daughter-ion yields and minimal loss in overall ion current compared to the ion current for protonated or cationized parent molecules. The major daughter ions for 10 pg of Aldicarb and penicillin G could be detected (signal-to-noise ratio greater than 5) under full-scan CAD conditions.

The effects of reactant vibrational, fine structure, and collision energy on the reactions of OCS+ with C2H2: Complementary studies of reactions in the [C2H2+OCS]+ system

Resonance-enhanced multiphoton ionization has been used to create state-selected OCS+ ions, which are then reacted with C2H2 in a guided-beam tandem mass spectrometer. OCS+ can be produced with excitation in all three of its vibrational modes, in either the upper or lower fine structure electronic state. Absolute cross sections for all product channels (C2H+2, C2HnS+(n=1, 2), and S+) are reported as a function of collision energy and vibrational state in the range from 0.06–4.5 eV. Different modes of nuclear motion have markedly different effects on reactivity and branching ratios. Production of C2H2S+, is the major chemical reaction channel, and its formation is strongly inhibited by collision energy, but only weakly affected by vibrational and fine structure state. The cross section for charge transfer (CT) shows vibrational effects that change with collision energy. For collision energies below 0.3 eV, CT is enhanced by all forms of nuclear motion, while at higher energies CT is weakly enhanced by C–S stretching, strongly enhanced by C–O stretching, and inhibited by bending. Both C2HS+ and S+ are minor channels, which turn on at higher collision energies. They are weakly affected by vibrational energy and fine structure state. These results are compared with those from our complementary study [T. M. Orlando, B. Yang, Y. Chiu, and S. L. Anderson, J. Chem. Phys. 92 7356 (1990)] of the other charge state of the [C2H2+OCS]+ system: reactions of C2H+2 with OCS. This allows comparison of the effects of 12 different reactant internal energy states on the same product channels.

Vibrational energy transfer in symmetric N2 charge transfer

Results of the crossed-beam investigation of the symmetric charge-transfer reaction of N2+ (X2Σg, ν = 0) with N2 (X1Σg, ν = 0) near 10 eV collision energy showed a symmetrically resonant channel with Δν = 0 as well as a series of inelastically scattered channels. Upon deconvolution to remove the Δν = 0 contribution, the inelastic Δν = 1, 2, and 4 channels were readily observed.

Collision energy, collision gas and collision gas pressure effects on the formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,7,8-tetrabromodibenzo-p-dioxin product ions

The effects of collision energy, the nature of the collision gas, and collision gas pressure on formation of product ions of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrabrominated dibenzo-p-dioxin (TBDD) and approaches to determine optimum conditions for mass spectrometry/mass spectrometry (MS/MS) of TCDDs ant TBDDs were investigated. The results demonstrate the optimum collision energy conditions are dependent on the pressure of argon, nitrogen, and xenon and independent of helium pressure

Analysis of the energy window for the quantum-state and angular scattering specificity in Ar + charge transfer with N 2

Previous kinematic analysis of the charge-transfer reaction of Ar + with N 2 has shown an energy window near 1 eV collision energy where quantum-specific and angular-specific scattering is observed. Reactant energy and angular distributions were used to determine the center-of-mass energy distribution from the nominal center-of-mass energies previously reported. The resultant distributions show that the maximum width of the energy “window” is 0.31 eV with a median collision energy of 0.91 eV rather than a width of 0.9 eV with a median energy near 1 eV as previously reported.

OH product state distribution and absolute reactive cross section for the reaction H(2.57 eV)+NO→OH+N

Photolysis of HBr with an ArF excimer laser at 193 nm yields H-atoms with high translational energy (2.57 eV), which can react with NO to form OH and N. The nascent OH rotational and fine structure state distributions were measured by laser-induced fluorescence probing the (A-X) system of OH in the near UV around 308 nm. A high degree of rotational excitation in the OH radicals formed was found, with 45% of the available excess energy being distributed among the rotational degrees of freedom of the OH products. The A-doublet distributions show higher population of the symmetrical OH(A') component, suggesting preference of a planar reaction mechanism with in-plane rotation of the HNO intermediate. Spinorbit states Π 1/2 and Π 3/2 are found to be statistically populated. From Doppler profiles, OH translational energies were obtained and found to be in agreement with the values expected from conservation of energy and momentum. Vibrational excitation of OH radicals, barely accessible at the collision energy used in our experiments, could not be observed. With a calibration method using H 2 O 2 photolysis as a well defined source of OH radicals, an absolute reactive cross section of σ=(0.01±0.005) 2 could be determined for the reaction H+NO→OH+N at 2.57 eV collision energy.

Collision energy effects in the Cs+ICH3→CsI+CH3 reaction

Differential and total reaction cross sections for the Cs+ICH3→CsI+CH3 system have been measured as a function of the collision energy by using the crossed beam technique. The analysis of the center-of-mass angular and recoil velocity distribution of the products indicated: (a) a backward peak character corresponding to a direct rebound mechanism at low collision energy; (b) over the collision energy range from 0.15 up to 0.56 eV, the backward character shifts to near sideways scattering. A direct interaction with product repulsion (DIPR) model analysis of this collision energy evolution showed an increasing participation of bent transition state configurations, which might be in competition with the purely collinear one at lower collision energy; (c) that the average products’ translational energy Ē′T increases approximately linearly with increasing collision energy ĒT as follows: Ē′T/kJ mol−1 =0.62 ĒT/kJ mol−1+58.5. Complete laboratory differential reaction cross-section measurements were carried out at 21 different relative velocities, then integrated and normalized to yield the total flux and reaction cross section in relative units. Over the available range of ET, σR(ET) shows a minimum at ET≂0.23 eV. A comparison of the present excitation function shape with current theoretical treatments is also reported.

Collision-induced decomposition of ions

The current status of the understanding of the collision-induced decomposition (CID) of di- and polyatomic ions is reviewed. The fundamental aspects of the CID of diatomic ions is considered in detail as a basis for the understanding of the processes leading to the CID of polyatomic ions. Particular attention is given to experimental and thoeretical work regarding the CID of diatomic ions via vibrational excitation and low energy CID (collision energy < 400 eV). The evidence for the low cross section for vibrational excitation by direct momentum transfer is emphasized. The knowledge concerning the CID of the polyatomic ions is more qualitative in nature. The experimental work on the effects of collision gas and collision energy on CID spectra and concerning the nature of the energy deposition process are reviewed. In conclusion the analytical aspects of the CID are considered and the influence of both the fundamental collision processes and instrumental characteristics on the final appearance of the CID spectra is emphasized.

A beam scattering study of the dynamics of CH+4(CH4,CH3)CH+5 reaction in the eV collision energy range: Three competing mechanisms of CH+5 formation

A crossed-beam study of the reaction CH+4(CH4,CH3)CH+5 was carried out in the collision energy range 0.6–2.3 eV. Three distinct patterns were observed, which may be interpreted in terms of three competing mechanisms for CH+5 formation: proton stripping, H-atom pickup, and intermediate complex decomposition. The existence of a C2H+8 intermediate, stable towards dissociation, is suggested by the results. The relative weights of the three mechanisms were estimated as a function of collision energy.

A crossed beam study of the ionization of molecules by metastable neon atoms

Total ionization cross sections for the collisions between metastable Ne*(3P2,0) atoms (predominantly 3P2) and several molecules (N2, CO, O2, NO, HCl, HBr, Cl2, CO2, N2O, CH4, CH3Cl, CH3Br, C2H6, C2H4, and C2H2) have been measured, in a crossed beam experiment, within the ≈ 0.03 to ≈ 0.5 eV collision energy range. The cross sections have been obtained on the same relative scale for all systems and calibrated to an absolute value by assuming a literature value for the reference system Ne*-Ar. These experimental cross sections have been integrated over the Maxwell-Boltzmann distribution to estimate the values of the ionizationrate constants. Comparison between the ionization and the quenching rate constants shows that the ionization is the main channel for the quenching of metastable neon atoms in thermal systems.

The effects of different vibrational modes and collision energy on the reaction of acetylene cations with carbonyl sulfide

Resonance-enhanced multiphoton ionization has been used to produce beams of vibrationally state-selected acetylene cations. The ions are formed with excitation in either the symmetric C–C stretch (ν2) or in a bending mode (ν5). Reactions with OCS have been studied in a guided ion-beam mass spectrometer. Absolute cross sections for the production of OCS+ and C2HnS+ (n=1,2) are reported for collision energies ranging from 80 meV to 5 eV. Charge transfer is observed to be enhanced by bending excitation, suppressed by C–C stretching vibration, and only weakly affected by collision energy. In contrast, the C2HnS+ channels are strongly collision energy dependent, with vibrational effects that vary with collision energy. The effects of bending and stretching excitation are qualitatively similar; however, the size of the effects are different and are not what would be expected on energetic grounds. These results are contrasted to the situation for reaction of mode selectively excited C2H+2 with methane.

Classical trajectory calculations for the D+H 2( v=0, j=0−3)→HD( v′, j′)+H reaction: Differential and state-to-state cross sections in the 0.35–1.10 eV collision energy range

Differential and total state-to-state cross sections for the D + H 2 ( v=0, j=0−3) → HD ( v′, j′) + H reaction in the 0.35–1.10 eV collision energy range, have been calculated on the LSTH surface using the QCT method. The results are commented on and compared to recent quantum mechanical calculations and to experimental measurements.

Effect of collision gas pressure and collision energy on reactions between oxygen and the negative molecular ion of tetrachlorodibenzo‐p‐dioxins in the collision cell of a triple ‐quadrupole mass spectrometer

AbstractLow‐energy reactive collisions between the negative molecular ion of a tetrachlorodibenzo‐p‐dioxin (TCDD) and oxygen inside the collision cell of a triple‐stage quadrupole mass spectrometer produce a substitution ion [M  Cl + O]−, a phenoxide ion [C6H4‐nO2Cln]−·, [M  HCl]−·, and Cl− by which 1,2,3,4‐, 1,2,3,6/1,2,3,7‐ and 2,3,7,8‐TCDD isomers can be distinguished either directly or on the basis of intensity ratios. The collision conditions have an important effect on the relative abundances. Energy‐ and pressure‐resolved curves show that the ions formed by a collisionally activated reaction (CAR) process, i.e. [M  Cl + O]− and [C6H4‐n,O2Cln]−·, are favoured by a high pressure of oxygen (3‐6 mTorr) (1 Torr = 133.3 Pa) and a low collision energy (0.1‐7 eV), whereas the ions formed by a collisionally activated dissociation (CAD) process, i.e. [M  HCl]−· and Cl−, are favoured by high pressure and high energy. By choosing a relatively low collision energy (5 eV) and high pressure (4 mTorr), the CAR and CAD ions can be clearly detected.

Collisionally activated dissociation: Effect of collision energy and collision cell pressure

Selective reaction monitoring data of the parent ion m/z 511 [M-pentafluorobenzyl]− and the four most abundant daughter ions (m/z 421, 331, 287, and 243) of 11-dehydro-thromboxane B2 pentafluorobenzylester (PFB)/bis-trimethylsilylether (TMS) are presented. Collision energy varied from 5 to 30 eV and argon collision cell pressure from 0.07 to 0.56 Pa. Results show that fragmentation is more dependent on target thickness than on collision energy. Maximum intensity of the daughter ion m/z 243 was obtained at 15-20 eV collision energy and 0.27 Pa collision cell pressure.

Internal energy effects in the collision‐induced dissociation of large biopolymer molecular ions produced by electrospray ionization tandem mass spectrometry of cytochrome c

AbstractThe effects of internal energy upon metastable and collision‐induced dissociation (CID) processes observed in the tandem mass spectrometry of multiply protonated molecules of horse‐heart cytochrome c (Mr 12360) are described. The internal energy of the multiply protonated (15H+) molecules (at m/z 825) formed by electrospray ionization (ESI) was manipulated using electric fields in the atmospheric pressure/vacuum interface region. Highly efficient CID is obtained for molecular ions collisionally activated in the ESI interface. The dissociation efficiency at 3.8 eV to 5.8 eV (center of mass) collision energies for internally “hot” molecular ions under multiple collision conditions in a triple quadrupole mass spectrometer is shown to be much greater than for “cold” ions. The CID spectra show dramatic effects due to internal energy, with charge stripping dominating for cold ions (where CID efficiency is very low) and extensive fragmentation observed for hot ions.

Collision target-gas effects during the tandem secondary-ion mass-spectrometric analysis of polymers

A triple-quadrupole secondary-ion mass spectrometer has been designed in order to study the fragmentation of secondary ions ejected from solid surfaces under low primary beam flux conditions (static SIMS). This system has been used to study the fragmentation of some simple polymers in order to identify some of the key parameters controlling the collisionally activated dissociation (CAD) process for secondary ions and to make comparison with observations made for conventional mass spectrometers. A variety of collision targets have been employed, including argon, xenon, sulphur hexafluoride and oxygen and the effects of target pressure and collision energy have been studied, for cluster ions generated from polytetrafluoroethylene (PTFE). Xenon provided the most complete fragmentation patterns. It has proved possible to construct complex fragmentation patterns and to observe ion–molecule reactions between fluorocarbon parent ions and oxygen and sulphur hexafluoride targets.

Tandem mass spectrometry of leucine enkephalin and physalaemin using a hybrid instrument

Daughter ion mass spectral data of [M + H]+ ions of leucine enkephalin and physalaemin, which were formed by fast atom bombardment, were obtained using an instrument of EBQQ configuration. In the case of leucine enkephalin, experiments were carried out in which the collision energy was varied and the collision gas pressure kept constant and vice versa. The results show that conditions can be established under which seuqence-relevant ions above m/z 200 are formed, as well as under which mainly immonium and acylium type ions are generated. Of possible interest for characterization of unknown peptides, when using hybrid instruments, are the mid-chain cleavage ions, which, at a constant argon gas pressure of 5 × 10−6 mbat, were found to maximize at around 30 eV collision energy. Daughter ion mass spectral data are also presented for [M + H]+ ions of physalaemin (mol. wt 1264). Compared to data obtained for physalaemin on multisector instruments, our results indicate that the formation of mid-chain cleavage ions is clearly enhanced.

Probing chemical reaction dynamics by rotational spectroscopy: The OH rotational distribution in the reaction H+O 2→OH+O

Pure rotational transitions have been used to probe high rotational states of OH(X 2Π, ν=0) formed in the reaction H+O 2→OH+O at 2.6 eV collision energy. The infrared diode absorption/gain technique is complementary to laser-induced fluorescence (LIF) and particularly useful for probing those high rotational levels where predissociation of the A 2Σ + state of OH limits the accuracy of LIF data. The rotational distribution is monotonically decreasing at N⪢25 in the title reaction, where trajectory calculations had suggested a local maximum.