Reactions of N2(A3Σ)

N₂(A³Σ), the lowest electronically excited state of N₂, has a long and distinguished history due to its role in nitrogen discharges and the nitrogen afterglow. Recently, the production of N₂(A) via photolysis and chemiluminescent reactions has been newly explored, and new facets of its reactivity have been uncovered. N₂(A) is unusual, in that its deactivation probability in collision with small molecules spans many orders of magnitude, and is frequently strongly dependent on the vibrational content of N₂(A). This behavior and the observed product channels can be understood in terms of a simple model for the energy transfer process. Brief comparison with reactions of related species is made.     

The temperature dependence and the mechanism of the SO2 (3B1) quenching reactions

The Arrhenius parameters have been determined for the SO₂(³B₁) quenching reaction (9), SO₂(³B₁) + M → (SO₂ ? M), for 21 different molecules as quenching partner M. The rate constants were calculated from phosphorescence lifetime measurements made over a range of reactant pressures and temperatures. Excitation of the SO₂ (³B₁) molecules was accomplished by two very different methods: (1) a 3829 Å laser pulse generated the triplet directly through absorption within the “forbidden” SO₂ (³B₁) → SO₂ (¹A₁) band; (2) a broadband Xe-flash system generated SO₂(³B₁) molecules and triplets were formed subsequently by intersystem crossing, SO₂(¹B₁) + M → SO₂(³B₁) + M. The measured rate constants were independent of the method of triplet formation employed. For the atmospheric gases, the activation energies (kcal/mole) were identical within the experimental error: N₂, 2.9 ± 0.4; 0₂, 3.2 ± 0.5; Ar, 2.8 ± 0.6; CO₂, 2.8 ± 0.4; CO, 2.7 ± 0.4; CH₄, 2.5 ± 0.6. This energy corresponds to the first region of the SO₂(³B₁) → SO₂(¹A₁) absorption spectra in which Brand and coworkers observe strong perturbations. It is suggested that the quenching in these cases results largely from the physical process involving potential energy surface crossing to another electronic state. Activation energies for SO₂(³B₁) quenching by the paraffinic hydrocarbons show a regular decrease in the series ethane, neopentane, propane, n-butane, cyclohexane, and isobutane, which parallels closely the decrease in C? H bond energies in these compounds. These and other data are most consistent with the dominance of chemical quenching in these cases. The rate constants for the olefinic and aromatic hydrocarbons and nitric oxide show only very small variations with temperature change, and they are near the kinetic collision number. These data support the hypothesis that quenching in these cases is associated with the formation of a charge-transfer complex and subsequent chemical interactions between the SO₂(³B₁) molecule and the π-system of these compounds.     

Deactivation of O2(A3Σ) by O2, O,and Ar

O₂ in the A³Σ_u⁺ state has been prepared in a discharge flow system by recombining oxygen atoms on a nickel surface. The decay of this excited state was followed by observing the emission between 280 and 400 nm. The wall deactivation was observed to approach unit efficiency. Rate constants were determined to be 0.9 × 10^?11, 2.9 × 10^?13, and 8.6 × 10^?16 cm³/molecule sec for the quenching of O₂(A³Σ_u⁺) by O, O₂, and Ar, respectively.     

Kinetic study of N2(B3Πg, υ) quenching by laser-induced fluorescence

The quenching kinetics of N₂(B³Π_g, υ) have been determined in a low-pressure flow system in the absence of N atoms. Individual vibrational levels of the B state were populated by laser pumping (first-positive bands) of N₂(A³Σ_u⁺) molecules. The latter were created upstream by energy transfer from Ar metastable atoms.     

Quenching of N2(A3Σu+) by O2, O,N, and H

Metastable N₂(A³Σ_u⁺), υ = 0, υ = 1, molecules are produced by a pulsed Tesla-type discharge of a dilute N₂/Ar gas mixture. Rate coefficients for quenching these metastable levels by O₂, O, N, and H were obtained by time-resolved emission measurements of the (0, 6) and (1, 5) Vegard–Kaplan bands. In units of cm³/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N₂(A³Σu⁺) are Within the limits of error these coefficients apply to quenching N₂(A³Σ_u⁺) υ′ = 1 as well.     

Ab initio CI study of the nitric oxide dimer (N2O2)

Configuration interaction (CI) studies of the ground and electronically excited states are reported for nitric oxide dimer (N₂O₂) in itscis equilibrium geometry. The lowest triplet state (³ B ₂) is found to lie only 0.43 eV above the ground state (¹ A ₁). The¹ A ₁ ¹ B ₁ transition is shown to be responsible for the rising absorption in the near infrared region observed experimentally. The transition of¹ A ₁¹ A ₂ calculated in the visible spectrum range of 701 nm (1.77 eV) is symmetry forbidden.     

Darstellung und Kristallstruktur von Diamminmagnesiumdiazid Mg(NH3)2(N3)2

Preparation and Crystal Structure of Diammin Magnesium Diazide Mg(NH₃)₂(N₃)₂ Diammin magnesium diazide was synthesized from Mg₃N₂ and NH₄N₃ in liquid ammonia and crystallized at 150 °C under autogenous atmosphere of HN₃ and NH₃ using sealed ampoules. Mg(NH₃)₂(N₃)₂ is a colorless, microcrystalline powder which can detonate above 180 °C. Caution, preparation and manipulation of Mg(NH₃)₂(N₃)₂ is very dangerous! The crystal structure was solved from powder data using the Patterson method and a Rietveld refinement was performed (Mg(NH₃)₂(N₃)₂, I 4/m, no. 87; a = 6.3519(1), c = 7.9176(2) Å; Z = 2, R(F²)= 0.1162). The crystal structure of Mg(NH₃)₂(N₃)₂ is related to that of SnF₄. It consists of planes built up from corner sharing Mg(NH₃)₂(N₃)₄ octahedra connected equatorially over their four azide bridges with the ammonia ligands being in trans position. IR data were collected and interpreted in accordance with the structural data.     

Preparation and Structure of Melemium Melem Perchlorate HC6N7(NH2)3ClO4·C6N7(NH2)3

A new perchlorate salt of melem (2,6,10‐triamino‐s‐heptazine, C₆N₇(NH₂)₃) was obtained from an aqueous solution of HClO₄ at lower concentration than the ones reported for the synthesis of melemium perchlorate monohydrate (HC₆N₇(NH₂)₃)ClO₄·H₂O. The new salt was identified as melemium melem perchlorate (HC₆N₇(NH₂)₃)ClO₄·C₆N₇(NH₂)₃ representing a melem adduct of water free melemium perchlorate. The crystal structure was solved by single‐crystal X‐ray methods ( , no. 2, Z = 2, a = 892.1(2), b = 992.7(2), c = 1201.5(2) pm, α = 112.30(3), β = 96.96(3), γ = 95.38(3)°, V = 965.8(4)·10⁶ pm³, 4340 data, 387 parameters, R1 = 0.039). Melemium melem perchlorate crystallizes in a layer‐like structure containing both protonated HC₆N₇(NH₂)₃ and non protonated C₆N₇(NH₂)₃ moieties in the coplanar layers as well as perchlorate ions between them, all of which being interconnected by hydrogen bonds. Vibrational spectroscopic investigations (FTIR and Raman) of the salt were conducted.     

The X˜1A1, a˜3B1, a˜1B˜1, and B˜1A1 electronic states of SiH2

Four electronically low-lying states of silylene (SiH₂) have been studied systematically using high level ab initio electronic structure theory. Self-consistent field (SCF), two-configuration (TC) SCF, complete active space (CAS) SCF, configuration interaction with single and double excitations (CISD), and CASSCF second-order (SO) CI levels of theory were employed with eight distinct basis sets. The zeroth-order wave functions of the ground (X˜ ¹A₁ or 1 ¹A₁) and B˜ ¹A₁ (or 2 ¹A₁) excited states are appropriately described by the first and second eigenvectors of the TCSCF secular equations. The TCSCF-CISD, CASSCF, and CASSCF-SOCI wave functions for the B˜ ¹A₁ (or 2 ¹A₁) state were obtained by following the second root of the CISD, CASSCF, and SOCI Hamiltonian matrices. At the highest level of theory, the CASSCF-SOCI method with the triple zeta plus triple polarization augmented with two sets of higher angular momentum functions and two sets of diffuse functions basis set [TZ3P(2f,2d)+2diff], the energy separation (T₀) between the ground (X˜ ¹A₁) and first excited (a˜ ³B₁) states is determined to be 20.5 kcal/mol (0.890eV,7180cm⁻¹), which is in excellent agreement with the experimental T₀ value of 21.0 kcal/mol (0.910eV,7340cm⁻¹). With the same method the T₀ value for the a˜ ¹B₁−X˜ ¹A₁ separation is predicted to be 45.1 kcal/mol (1.957 eV,15780 cm⁻¹), which is also in fine agreement with the experimental value of 44.4 kcal/mol (1.925 eV,15530 cm⁻¹). The T₀ value for the B˜ ¹A₁−X˜ ¹A₁ separation is determined to be 79.6 kcal/mol (3.452 eV,27 840 cm⁻¹). After comparison of theoretical and experimental T₀ values for the a˜ ³B₁ and a˜ ¹B₁ states and previous studies, error bars for the B˜ ¹A₁ state are estimated to be ±1.5 kcal/mol (±525 cm⁻¹). The predicted geometry of the B˜ ¹A₁ state is r_e(SiH)=1.458 and θ_e=162.3^∘. The physical properties including harmonic vibrational frequencies of the B˜ ¹A₁ state are newly determined. Received: 10 March 1997 / Accepted: 2 April 1997     

A kinetic study of the chemistry of the SO2 (3B1) reactions with cis- and trans-2-butene

The chemical reactions of SO₂(³B₁) molecules with cis- and trans-2-butene have been studied in gaseous mixtures at 25°C by excitation of SO₂ within the SO₂(³B₁) → SO₂(+, ¹A₁) ‘forbidden’ band using 3500–4100-Å light. The initial quatum yields of olefin isomerization were determined as a function of the [SO₂]/[2-butene] ratio and added gases, He and O₂. The kinetic treatment of these data suggests that there is formed in the SO₂(³B₁) quenching step with either cis- or trans-2-butene, some common intermediate, probably a triplet addition complex between SO- and olefin. It decomposes very rapidly to form the 2-butene isomers in the ratio [trans-2-butene]/[cis-2-butene] = 1.8. In another series of experiments SO₂ was excited using a 3630 ± 1-Å laser pulse of short duration, and the SO₂(³B₁) quenching rate constants with the 2-butenes were determined from the SO₂(³B₁) lifetime measurements. The rate constants at 21°C are (1.29 ± 0.18) × 10¹¹ and (1.22 ± 0.15) × 10¹¹ l/mole·sec with cis-2-butene and trans-2-butene, respectively, as the quencher molecule. Within the experimental error these quenching constants equal those derived from the quantum yield data. Thus the rate-determining step in the isomerization reaction is suggested to be the quenching reaction, presumably the formation of the triplet SO₂-2-butene addition complex. In a third series of experiments using light scattering measurements, it was found that the aerosol formation probably originates largely from SO₃ and H₂SO₄ mist formed following the reaction SO₂(³B₁) + SO₂ → SO₃ + SO(³Σ^?). Aerosol formation from photochemically excited SO₂-olefin interaction is probably unimportant in these systems and must be unimportant in the atmosphere.     

Über das Tri(phosphorano)borazinium-Monokation [H3B3(NPEt3)3Cl2]+. Kristallstrukturen von Me3SiNPR3 · BH3 (R = Et,Ph), [H3B3(NPEt3)3Cl1,85Br0,15]Br · CCl4 und des Hydrolyseproduktes NH4[B5O6(OH)4] · 2 H2O

On the Tri(phosphorano)borazinium Monocation [H₃B₃(NPEt₃)₃Cl₂]⁺. Crystal Structures of Me₃SiNPR₃ · BH₃ (R = Et, Ph), [H₃B₃(NPEt₃)₃Cl_1.85Br_0.15]Br · CCl₄, and of the Product of Hydrolysis NH₄[B₅O₆(OH)₄] · 2 H₂O The crystal structures of the donor-acceptor complexes of the silylated phosphanimines with borane which are suitable as educts for the synthesis of tri(phosphorano)borazinium ions, Me₃SiNPR₃ · BH₃ (R = Et, Ph), are described. After addition of CCl₄ the reaction of Me₃SiNPEt₃ with HBBr₂ · SMe₂ in CH₂Cl₂ leads to the tri(phosphorano)borazinium monocation [H₃B₃(NPEt₃)₃Cl₂]⁺, which is characterized crystallographically as [H₃B₃ · (NPEt₃)₃Cl_1.85Br_0.15]Br · CCl₄. It complements the series of the tri(phosphorano) cations [H₃B₃(NPEt₃)₃]³⁺ and [H₄B₃(NPEt₃)₃]²⁺ by the monocation. NH₄[B₅O₆(OH)₄] · 2 H₂O can be isolated as product of hydrolysis of the tri(phosphorano)borazinium ions; its crystal structure is redetermined, because in the literature it is based on a wrong space group. Me₃SiNPEt₃ · BH₃ ( 1 ): Space group P1, Z = 4, lattice dimensions at 213 K: a = 710.9(4), b = 1465.9(3), c = 1536.0(3) pm, α = 107.05°, β = 99.40(3)°, γ = 97.41(3)°; R = 0.0740. Me₃SiNPPh₃ · BH₃ ( 2 ): Space group P2₁/c, Z = 4, lattice dimensions at 203 K: a = 934.6(1), b = 1398.6(1), c = 1626.1(1) pm, β = 103.52(1)°; R = 0.0556. [H₃B₃(NPEt₃)₃Cl_1.85Br_0.15]Br · CCl₄ ( 3 ): Space group P2₁/n, Z = 4, lattice dimensions at 223 K: a = 1237.9(3), b = 1214.1(3), c = 2402.4(4) pm, β = 93.52(1)°. 3 holds a B₃N₃ six-membered ring in a distorted boat conformation. NH₄[B₅O₆(OH)₄] · 2 H₂O ( 4 ): Space group Aba2, Z = 4, lattice dimensions at 273 K: a = 1131.3(1), b = 1103.0(1), c = 923.0(1) pm; R = 0.0564.     

Phosphaniminato-Komplexe von Bor. Synthese und Kristallstrukturen von [BBr2(NPMe3)]2, [B2Br3(NPiPr3)2]Br, [B2(NPEt3)4]Br2, [B2Br2(NPPh3)3]BBr4 und [{B2(NMe2)2}2(NPEt3)2]Cl2

Phosphoraneiminato Complexes of Boron. Syntheses and Crystal Structures of [BBr₂(NPMe₃)]₂, [B₂Br₃(NPⁱPr₃)₂]Br, [B₂(NPEt₃)₄]Br₂, [B₂Br₂(NPPh₃)₃]BBr₄ and [{B₂(NMe₂)₂}₂(NPEt₃)₂]Cl The bromoderivatives of the title compounds are prepared from the corresponding silylated phosphoraneimines Me₃SiNPR₃ and boron tribromide. The boron subcompound [{B₂(NMe₂)₂}₂(NPEt₃)₂]Cl₂ derives from Me₃SiNPEt₃ and B₂Cl₂(NMe₂)₂. All complexes are characterized by NMR and IR spectroscopy as well as by crystal structure determinations. [BBr₂(NPMe₃)]₂ (1): Space group P2₁/n, Z = 2, R = 0.031. Lattice dimensions at ?50°C: a = 723.8, b = 894.2, c = 1305.4 pm, β = 92.35°. 1 forms centrosymmetric molecules in which the boron atoms are linked via μ₂-N bridges of the NPMe₃^? groups of from B₂N₂ four-membered rings with B? N distances of 149.9 and 150.9 pm. B₂Br₃(NPⁱPr₃)₂]Br (2): Space group P2₁, Z = 2, R = 0.059. Lattice dimensions at ?80°C: a = 817.6, b = 2198.7, c = 851.5 pm, β = 115.09°. In the cations of 2 the boron atoms are lined via the μ₂-N atoms of the NPⁱPr₃^? groups to form planar, asymmetric B₂N₂ four-membered rings with B? N distances of 143 and 156 pm. [B₂(NPEt₃)₄[Br₂·4CH₂Cl₂ (3): Space group C2/c, Z = 4, R = 0.042. Lattice dimensions at ?50°C: a = 1946.1, b = 1180.3, c = 2311.3 pm, β = 101.02°. The structure contains centrosymmetric dications in which both the boron atoms are lined by the N atoms of two of the NPEt₃^? groups to form a B₂N₂ four-membered ring with B? N distances of 149.6 pm. The remaining two NPEt₃^? groups are terminally bonded with very short B? N distances of 133.5 pm. B₂Br₂(NPPh₃)₃]BBr₄ (4): Space group P1 , Z = 2, R = 0.065. Lattice dimension at ?50°C: a = 1025.7, b = 1496.1, c = 1807.0 pm, α = 85.09°, β = 82.90°, γ = 82.72°. In the cation the boron atoms are lined via the μ₂-N atoms of two of the NPPh₃^? groups to form a nearly planer B₂N₂ four-membered ring with B? N distances of 149.3-153.1 pm. The third NPPh₃³ group is terminally connected with teh sp² hybridized boron atom and with a B? N distance of 134.1 pm along with an almost linear BNP bond angle of 173.6°. [{B₂(NMe₂)₂}₂(NPEt₂)₂]Cl₂ · 3CH₂Cl₂ (5): Space group C2/c, Z = 4, R = 0.098. Lattice dimensions at ?70°C: a = 1557.9, b = 1294.7, c = 2122.9 pm, β = 96.08°. The structure of 4 contains centrosymmetric dications in which two by two B-B dumb-bells are linked via the μ₂-N atoms of the two NEPt₃^? groups to form B₄N₂ six-membered rings with B? N distances of 150 and 156 pm and B-B distances of 173 pm. The B? N distances of the terminally bonded NMe₂^? groups correspond to 138 pm double bonds.     

Theoretical rotational-vibrational spectra of theX 3 B 1,a 1 A 1 andb 1 B 1 states of NH 2 +

Summary The three-dimensional potential energy functions have been calculated from highly correlated multireference configuration interaction electronic wavefunctions for theX ³ B ₁,a ¹ A ₁, andb ¹ B ₁ states of the NH ₂ ⁺ ion. For the quasi-linear electronic ground state this information and the electric dipole moment functions have been used to calculate spectroscopic constants, line intensities and rotationally resolved absorption spectra. For thea ¹ A ₁-b ¹ B ₁ bent/quasi-linear Renner-Teller system ro-vibronic energy levels have been obtained from a variational approach accounting for anharmonicity, rotation-vibration and electronic angular momenta coupling effects. The vibronic levels are given for energies up to 13 500 cm^–1 for the bending levels and up to 8000 cm^–1 for the stretching and combination levels.Dedicated in the honor of Prof. Werner Kutzelnigg     

Two new XP(O)[NHC(CH3)3]2 phosphoramidates,with X = (CH3)2N and [(CH3)3CNH]2P(O)(O)

In N,N′‐di‐tert‐butyl‐N′′,N′′‐dimethylphosphoric triamide, C₁₀H₂₆N₃OP, (I), and N,N′,N′′,N′′′‐tetra‐tert‐butoxybis(phosphonic diamide), C₁₆H₄₀N₄O₃P₂, (II), the extended structures are mediated by P(O)...(H—N)₂ interactions. The asymmetric unit of (I) consists of six independent molecules which aggregate through P(O)...(H—N)₂ hydrogen bonds, giving R₂¹(6) loops and forming two independent chains parallel to the a axis. Of the 12 independent tert‐butyl groups, five are disordered over two different positions with occupancies ranging from to . In the structure of (II), the asymmetric unit contains one molecule. P(O)...(H—N)₂ hydrogen bonds give S(6) and R₂²(8) rings, and the molecules form extended chains parallel to the c axis. The structures of (I) and (II), along with similar structures having (N)P(O)(NH)₂ and (NH)₂P(O)(O)P(O)(NH)₂ skeletons extracted from the Cambridge Structural Database, are used to compare hydrogen‐bond patterns in these families of phosphoramidates. The strengths of P(O)[...H—N]_x (x = 1, 2 or 3) hydrogen bonds are also analysed, using these compounds and previously reported structures with (N)₂P(O)(NH) and P(O)(NH)₃ fragments.     

Pyrolysis of 2-phenylethylamines heats of formation of aminomethyl radicals R2NCH2 · (R = H,CH3)

A kinetic study of the very low-pressure pyrolysis of ethylbenzene (I), 2-phenylethylamine (II), and N,N-dimethyl 2-phenylethylamine (III) above 900 K yields the heats of formation of aminomethyl (A) and N,N-dimethylaminomethyl (B) radicals: ΔH_{?, 300 K}(A) = 30.3 and ΔH_{?, 300 K}(B) = 27.5 kcal/mol. The difference of stabilization energies E_s, (relative to methyl radicals): Δ = E_s(B) ? E_s(A) = (2 ± 1) kcal/mol, conforms to similar effects in methyl substituted alkyl and amino free radicals.     

Über das metallreiche Lanthannitridoboratnitrid La5(B2N4)N2

On the Metal‐rich Lanthanum Nitridoborate Nitride La₅(B₂N₄)N₂ La₅(B₂N₄)N₂ was synthesized by solid state reactions in fused tantalum containers from Li₃(BN₂), LaCl₃, Li₃N and La at 950 °C. The crystal structure refinement on a needle‐shaped single‐crystal yielded the monoclinic space group C2/m, the lattice parameters a = 1259.5(2), b = 368.53(4), c = 909.4(2) pm, β = 106.03(2)°, and R values of R1 = 0.041, wR2 = 0.066 for all independent reflections. The new compound La₅(B₂N₄)N₂ introduces the member with x = 2 to the formula type RE_3+x(B₂N₄)N_x (RE = rare earth, x = 0, 1). The structure contains the nitridoborate ion B₂N₄^8– that is isoelectronic with the oxalate ion and N^3–. Corresponding with (La³⁺)₅(B₂N₄)^8–(N^3–)₂(e^–) one additional electron is present.     

Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system,and the quenching of O2(1Σg+) by atomic hydrogen

The generation of metastable O₂(¹Σg⁺) and O₂(¹Δg) in the H + O₂ system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O₂(¹Σg⁺) and O₂(¹Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO₂(²A′₀₀₀) → HO₂(²A″₀₀₀), HO₂(²A′₀₀₁) → HO₂(²A″₀₀₀), and H O₂(²A″₂₀₀) → HO₂(²A″₀₀₀) emissions were detected in the H + O₂ system. The rate constants for the quenching of O₂(¹Σg⁺) by H and H₂ were determined to be (5.1 ± 1.4) × 10^?13 and (7.1 ± 0.1) × 10^?13 cm³ s^?1, respectively. An upper limit for the branching ratio to produce O₂(¹Σg⁺) by the H + HO₂ reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.     

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

Thermal Decomposition of CF3C(O)O2NO2, CClF2C(O)O2NO2, CCl2FC(O)O2NO2, and CCl3C(O)O2NO2

Haloacetyl, peroxynitrates are intermediates in the atmospheric degradation of a number of haloethanes. In this work, thermal decomposition rate constants of CF₃C(O)O₂NO₂, CClF₂C(O)O₂NO₂, CCl₂FC(O)O₂NO₂, and CCl₃C(O)O₂NO₂ have been determined in a temperature controlled 420 l reaction chamber. Peroxynitrates (RO₂NO₂) were prepared in situ by photolysis of RH/Cl₂/O₂/NO₂/N₂ mixtures (R = CF₃CO, CClF₂CO, CCl₂FCO, and CCl₃CO). Thermal decomposition was initiated by addition of NO, and relative RO₂NO₂ concentrations were measured as a function of time by long-path IR absorption using an FTIR spectrometer. First-order decomposition rate constants were determined at atmospheric pressure (M = N₂) as a function of temperature and, in the case of CF₃C(O)O₂NO₂ and CCl₃C(O)O₂NO₂, also as a function of total pressure. Extrapolation of the measured rate constants to the temperatures and pressures of the upper troposphere yields thermal lifetimes of several thousands of years for all of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitrates may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rates. Results on the thermal decomposition of CClF₂CH₂O₂NO₂ and CCl₂FCH₂O₂NO₂ are also reported, showing that the atmospheric lifetimes of these peroxynitrates are very short in the lower troposphere and increase to a maximum of several days close to the tropopause. The ratio of the rate constants for the reactions of CF₃C(O)O₂ radicals with NO₂ and NO was determined to be 0.64 ± 0.13 (2σ) at 315 K and a total pressure of 1000 mbar (M = N₂). © 1994 John Wiley & Sons, Inc.     

Deactivation of I(2P1/2) by CH3Cl,CH2Cl2, CHCl3, CCl3F,and CCl4

Collisional deactivation of I(²P_1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH₃Cl, CH₂Cl₂, CHCl₃, CCl₃F, and CCl₄ are 3.1±0.3×10⁻¹³, 1.28±0.08×10⁻¹³, 5.7±0.3×10⁻¹⁴, 3.9±0.4×10⁻¹⁵, and 2.3±0.3×10⁻¹⁵cm³ molecule⁻¹ s⁻¹, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH₃Cl, CH₂Cl₂, and CHCl₃ reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm⁻¹) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998