Dissociative Excitation Reaction Research Articles

Threshold Ionization Mass Spectrometry of BrCN: Gas-Phase Reaction Channels Which Determine the Nitrogen Contents in Amorphous Carbon Nitride Films

The dissociative ionization process of BrCN was studied using the threshold ionization mass spectrometry. The threshold of the production of C+ was determined as 23.3±1.0 eV. From the discussion based on this result, the low (≤0.2) concentration of the N atoms in the amorphous carbon nitride films formed from the dissociative excitation reaction of BrCN with the electron cyclotron resonance plasma of Ar was considered to originate in the effective production of C and C+ by the impact of high-energy electrons.

Ion-Induced Processes in the Dissociative Excitation Reaction of BrCN to Synthesize Mechanically Hard Amorphous Carbon Nitride Films in the Microwave Plasma Chemical Vapor Deposition System

High-resolution emission spectra have been observed for the dissociative excitation reaction of BrCN with the microwave-discharge flow of Ar to synthesize mechanically hard a-CNx films. From the analysis of intensity of the CN(B2Σ+–X2Σ+) emission under the conditions of trapping charged species and the addition of SF6, BrCN is found to be excited via the charge transfer from Ar+ followed by the recombination of BrCN+ with thermal electrons as well as the energy transfer from Ar(3P0,2). The relative intensity of the resonance lines of Ar+ and Ar, IAr+ /IAr, has been measured under the RF-biased condition. The dependence of IAr+ /IAr on the RF-bias voltage is found to be strongly correlated with that of the reported hardness of films [Tanaka et al.: Jpn. J. Appl. Phys. 39 (2000) 4148], confirming the proposed mechanism of film hardening by the bombardment of the film surface by Ar+.

Mechanism of Formation of the CN(B2Σ+) State from Dissociative Excitation Reaction of BrCN with Electron Cyclotron Resonance Plasma of Ar

High-resolution emission spectra of the CN(B2Σ+–X2Σ+) transition and the resonance lines of Ar and Ar+ have been observed for the dissociative excitation reaction of BrCN with the electron cyclotron resonance (ECR) plasma of Ar. These spectra have been compared with those observed for the reaction with the microwave (MW) discharge flow of Ar. It is found that the energy transfer from the metastable state of Ar which proceeds predominantly in the MW discharge flow does not proceed in the ECR plasma. The electron density and temperature have been measured by an electrostatic-probe measurement, from which the kinetic analysis of formation of CN(B2Σ+) has been conducted. The most dominant process of formation of the CN(B2Σ+) state in the ECR plasma is considered to be the dissociative excitation of BrCN by the impact of high-energy free electrons, where the contribution of the recombination of BrCN+ with thermal free electrons cannot be excluded.

Limitation of Nitrogen Incorporation into the Hydrogenated Amorphous Carbon Nitride Films Formed from the Dissociative Excitation Reaction of CH3CN

High-resolution CN(B2Σ+–X2Σ+) and CH(A2Δ–X2Π) emission spectra were observed for the dissociative excitation reaction of CH3CN with the microwave-discharge flow of Ar for synthesizing hydrogenated amorphous carbon nitride (a-CNx:H) films. The simulation analysis of these spectra revealed that the relative number density of CH(A) to that of CN(B), NCH(A)/NCN(B), was strongly dependent on the pressure of Ar, PAr, in the range of PAr=0.1–0.8 Torr. The PAr-dependence of NCH(A)/NCN(B) showed a strongly negative correlation with that of the [N]/([N]+[C]) ratio obtained in our previous structural analysis of the films [Saitoh et al.: Jpn. J. Appl. Phys. 39 (2000) 1258]. This correlation was fully explained in terms of the consumption of the CN radical by the hydrogen-abstraction reaction from the film surface, preventing the incorporation of the nitrogen atoms into the a-CNx:H films.

Hardness and Structure of a-CNx Films Synthesized by Chemical Vapor Deposition

Mechanically hard a-CNx films were synthesized using a combination of ion bombardment and the chemical vapor deposition process using the dissociative excitation reaction of BrCN with Ar metastable atoms. Nanoindentation tests disclosed that the indentation hardness, Young's modulus and elastic recovery increased with increasing ion-accelerating voltage. Moreover, the degree of flow among clusters decreased in the ion-bombarded sample. The D (disordered)-band absorption on an infrared absorption spectrum was replaced by a C–N absorption assigned to the tertiary aromatic amine. These results suggest that the internal and external structures of the carbon nitride cluster change from the two-dimensional order to the three-dimensional order of C–N. The structure of hard a-CNx is clearly distinguishable from nitrogen-containing diamond-like carbon.

Mechanism of Nitrogen Incorporation into Amorphous-CNx Films Formed by Plasma-Enhanced Chemical-Vapor Deposition of the Doublet and Quartet States of the CN Radical

High-resolution CN(B2Σ+–X2Σ+) emission spectra were observed for the various processes to form amorphous-CNx (a-CNx) films using the plasma-enhanced chemical-vapor deposition of the CN radical produced from the dissociative excitation reactions of cyanides. A strong correlation was confirmed between the electronic states of CN in the plasma and the bonding states of nitrogen atoms in the films. The 4Σ+ and 4Π states of CN were the precursors of the one- and/or two-dimensional C=N and C–N network structures of the films with high nitrogen content, [N]/([N]+[C]) ≤0.5. The CN(X2Σ+) state formed the C≡N terminations primarily, a part of which changed to the one-dimensional C=N network from the additive reactions. The above correlation was fully explained by the molecular orbitals and the electronic configurations for the relevant electronic states of CN.

Synthesis of Amorphous Carbon Nitride Films Using Dissociative Excitation Reaction

In this investigation, we aim to produce highly nitrogen-doped carbon, so-called carbon nitride, films without the incorporation of hydrogen. In the physical vapor deposition process, irradiation by energetic nitrogen ions increases nitrogen content without the incorporation of hydrogen. In the chemical vapor deposition process, hydrogen should be included into the film due to the use of a hydrocarbon reactant. In this study, the synthesis of carbon nitride films having high nitrogen and low hydrogen contents was attempted using a chemical-vapor-deposition apparatus. First of all, a CH3CN+Ar mixture was selected as a reactant including hydrogen. Dehydrogenation of the reactant was carried out by plasma decomposition. Second, as a reaction system without hydrogen, BrCN+Ar was also selected for starting materials. The dissociative excitation reaction of cyanides with argon metastable atoms produces CN radicals, Ar(3P0,2)+BrCN →Ar+Br+CN(A2Πi, B 2Σ+, 4Σ+, 4Π). This finally proceeds to the deposition of CN radicals to form the carbon nitride film on a solid-state surface. When using the former reactant, large amounts of hydrogen remained in the amorphous carbon nitride films, although the amount of hydrogen varied with deposition conditions. The sample formed using the latter reactant was amorphous carbon nitride with very little hydrogen. The nitrogen fraction [N]/([N]+[C]) of the sample using the latter rectant is as high as ∼0.3, higher than those obtained from the samples synthesized with the former reactant.

B → X transitions in HgI caused by collisions of N2+ -CO^+ ions with HgI_2 molecules

Collision-induced dissociative excitation reactions involving collisions of N(+)(2) and CO(+) ions and HgI(2) molecules have been studied in the kinetic energy range of 100-1000 eV (laboratory frame). Emission spectra from the B ? X transition of the HgI radical as well as atomic mercury lines from various highly excited energy levels have been observed and analyzed. Emission cross sections of the most intense molecular band of the HgI([Equation]) transition at 445 nm have been determined.

Violet emission of cyanogen produced in the reaction of argon(3P0,2) with cyanogen bromide. 1. Nascent vibrational and rotational distributions of CN(B2.SIGMA.+)

The CN(B 2 Σ + -X 2 Σ + ) emission spectrum, produced in the dissociative excitation reaction of BrCN with Ar( 3 P 0,2 ) at thermal collision energy, was observed by using the flowing afterglow method. The effect of collisional relaxation of the excited electronic states of CN by the ground-state Ar atoms was minimized by lowering the ambient argon pressure to less than 10 mTorr. The «nascent» rovibrational distribution of CN(B 2 Σ + ) was determined by spectral simulation. A surprisal analysis of the nascent rovibrational distribution of CN(B 2 Σ + ) indicated that the dominant pathway of the reaction of BrCN with Ar( 3 P 0,2 ) was energy transfer, instead of argon complex formation of ion-pair exciplex formation

Product rotational alignment in the excitation transfer reaction Ar(3P2)+N2→Ar+N2(C 3Πu)

The velocity dependence of the N2(C) rotational alignment from the title excitation transfer reaction was studied over the collision energy range 42–460 meV, using a beam-gas time-of-flight method. The alignment was found to be positive, and to increase approximately linearly with energy: the extrapolated line has a large positive intercept, suggesting that the alignment persists down to zero energy. The present results, together with previous studies of this reaction, are consistent with a model in which the reaction occurs preferentially in the plane of rotation of the N2. It is suggested that this steric effect is due primarily to the orbital overlap requirements of the electron exchange mechanism. The polarization of the fluorescence from the dissociative excitation reactions of Ar*+CS2, Ar*+H2O, Kr*+CS2, and Xe*+BrCN was also measured and found to be zero at all velocities.

Collision energy dependence of the cross sections for the dissociative excitation reactions: Rg(3P0,2) +NH3→Rg+NH(A 3Π, c 1Π)+H2 (Rg=Ar, Kr)

The integral cross sections for the title reactions were determined for the relative collision energies between 0.3 and 1.4 eV by applying arc-heating metastable rare gas beams to a crossed molecular beam–time-of-flight (TOF) energy selection technique, in which product fluorescence intensities from both NH(A 3Π–X 3Σ−) and NH(c 1Π–a 1Δ) bands were monitored. With Ar(3P0,2 ) excitation, the relative branching fractions of nascent NH(A 3Π) and NH(c 1Π) formation were found to be invariant with the collision energy within the experimental error. With Kr(3P0,2) excitation, however, no apparent NH(c 1Π–a 1Δ) emission was observed, only emission from NH(A 3Π) was observed. The absolute cross section for formation of these nascent NH radicals was also determined. Collision energy dependence of the cross section for the reaction Ar (3P0,2) +NH3→Ar(1S0)+NH(A 3Π,c 1Π)+H2 was found to be negative, whereas that for the reaction Kr(3P0,2 )+NH3→Kr(1S0)+NH(A 3Π)+H2 showed positive dependence in the collision energy range studied. Possible mechanisms for the formation of NH(A 3Π,c 1Π) from Rg(3P0,2)+NH3 are discussed.

Rotational perturbations in the CN(B2Σ+–X2Σ+) tail band system. III. Molecular constants for the 4Π, 4Σ+, A2Πi, and X2Σ+ states

The CN(B2Σ+–X2Σ+) tail band system was observed by using the dissociative excitation reactions of HCN and BrCN with Ar(3P0.2) in an argon flowing afterglow. The following intensity anomalies owing to the B2Σ+ ~ 4Π rotational perturbations were analyzed: (νB, ν11) = (9,x), (11,x + 2), and (18,x + 13), where x is estimated to be 0 or 1. These anomalies, as well as(νB, ν11) = (12,x + 3), (14,x + 6), and (17,x + 11), were analyzed by spectral simulation. The CN(B2Σ+–X2Σ+) 14–14 band spectrum observed by Jenkins was re-analyzed, and the molecular constants for the perturbing 4Π state, the interaction constants, and the crossing schemes for the B2Σ+ ~ 4Π perturbations were determined. The intensity anomalies due to the perturbations by the 4Σ+, A2Πi, and X2Σ+ states were also observed: (νB, νΣ) = (15,p + 6), where p is estimated to be 8 ± 1, (νB, νA) = (11, 26) and (17, 34), and (νB, νX) = (11, 28). The molecular constants for the perturbing levels were estimated by a simulation analysis.

Mercury halide B(2Σ+) vibrational distributions from dissociative excitation reactions of Hg halides with Xe(3P2) and N2(A,3Σ+u)

The HgX(B 2Σ+–X 2Σ+), X=Cl, Br, I, spectra from the dissociative excitation reactions of N2(A 3Σ+u, v=0, 1) and Xe(3P2) with several mercuric and methylmercury halides have been simulated to assign the HgX(B) vibrational distributions. The distributions from the methylmercury halides could be described as Boltzmann types with temperatures ranging from 1000 K for N2(A)+CH3HgI to 9000 K for Xe(3P2)+CH3HgCl. The distributions from the mercuric halides are non-Boltzmann and the 〈fV〉 are somewhat higher than for the CH3HgX compounds. The initial HgX(B) vibrational distributions are used to discuss the state-to-state quenching mechanisms.

Quenching of N 2(A 3∑ +u) by Hg(II) halides

The flowing afterglow technique has been used to study the reactions of N 2(A 3∑ + u' v = 0, 1) with some methylmercury and mercuric halides. Room temperature quenching rate constants and rate constants for production of HgX(B 2∑ + were measured. Evidence is presented that shows another electronic state of N 2, besides N 2(A), can produce HgX(B) via dissociative excitation reactions with HgX 2.

Vibronic surprisal analysis of the dynamics of photodissociation and related reactions

Comparisons of experimentally observed product vibronic state distributions to statistically expected distributions indicate that intrafragment dynamics have primary importance in photodissociative and predissociative excitation reactions and in collision-induced electronic-to-vibrational energy transfer processes and that collisional dissociative excitation reactions probably involve sequential 2-body interactions rather than a concerted 3-body interaction.

Excitation of CN violet (B 2Σ+−X 2Σ+) and red (A 2Πi−X 2Σ+) bands by reaction of Ar and Xe metastable atoms with CN-containing compounds

The vibrational, and in some cases rotational, populations of the CN (A 2Πi) and (B 2Σ+) states produced by the dissociative excitation reactions of metastable argon and xenon atoms with HCN, ICN, and BrCN have been measured. Emission from the D, E, and F states of CN were observed from Ar(3P0,2) with BrCN. Anomalously high intensities from perturbed rotational levels of CN (B 2Σ+; v′ = 0, 11, 14) were found, and only the perturbed levels are produced from CNBr and CNI. The interaction of metastable argon atoms with BrCN and ICN gave excitation to v′ = 20 of CN (B 2Σ+) with a population inversion for v′ > 11 relative to lower levels. Extremely high rotational excitation of CN (B 2Σ+; v′ = 0, 1, 2) resulted from the interaction of Xe(3P2) with BrCN and ICN. The spectroscopic observations provide extensive detail and illustrate the complexity of these dissociative excitation reactions. In addition to a short discussion of the mechanism of interaction between the metastable atoms and CN compounds, some comments are offered concerning the spectroscopy of the CN red and violet emissions. Investigation of the electronic quenching of CN (B) emission showed an unusually high quenching rate for v′ = 11 by CNBr or CNI.

The emission spectrum of CS ( a3Π → X1Σ +) excited by interaction of CS containing molecules with metastable argon atoms

The energy transfer reactions of metastable argon atoms ( 3 P 0, 2) with SCS, SCO and SCCl 2 have been investigated in a fast flow system. Dissociative excitation reactions gave relatively intense emission from electronically excited CS( a 3Π; v′ ≤ 3). The intensity of the forbidden CS( a 3Π; v′ ≤ 3 → X 1Σ +) system from this source was sufficient to give improved band head assignments and spectroscopic constants; i.e., ω e ′ = 1139 ± 2 cm −1 and ω e ′ x e ′ = 9.7 ± 1 cm −1. Some new band heads were also observed and assigned as the 2-0, 2–4, 3-1, 3-3, 3–4 and 3–5 transitions. The low resolution did not allow an unambiguous interpretation of the spin-orbit coupling case of CS( a 3Π), although some analogies to CO( a 3Π → X 1Σ +) may be drawn. New, unassigned bands, which probably can be attributed to other CS triplet states, were observed in the region 4500–7500 Å and are briefly discussed.

Quenching processes and rate constants for interaction of metastable argon atoms with diatomic and triatomic molecules

The rate constants for quenching of metastable Ar(3P2) atoms by some diatomic and triatomic molecules have been measured in a discharge-flow apparatus at room temperature. The concentration of argon (3P2) atoms was monitored by absorption spectroscopy as a function of time and of concentration of various quenching gases. The rate constants varied from 1.5 to 50 × 10–11 cm3 molecule–1 s–1. The magnitudes of the rate constants are discussed in relation to the products observed in previous studies from this laboratory. Observations of the electronic quenching and vibrational relaxation of CS(a3Π) by CS2 and argon, respectively, are reported; the CS(a3Π) molecule was formed by the dissociative excitation reaction between Ar(3P2) and CS2.