Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

Microwave spectrum and structure of CF3OOCl

The microwave spectrum of chloroperoxytrifluoromethane has been recorded from 12.5 to 40.0 GHz. Only a-type transitions were observed. The R-branch assignments have been made for both the CF₃OO³⁵C1 and CF₃OO³⁷Cl species for the ground vibrational state. The rotational constants are: A=4808± 12, B=1318.55±0.02, C=1278.28±0.02 MHz for the ³⁵CI species, and A=4748±300,B=1285.28±0.96, C=1246.80±0.96 MHz for the ³⁷Cl species. From a diagnostic least-squares adjustment to fit the six rotational constants the following structural parameters were obtained: r(C-0)=1.377±0.03 Å, r(O-O)=1.445± 0.049 Å, r(Cl-O)=1.69±0.04 Å, ∠COO=108.1±4.2°, ∠ClOOC=99.5±2.0°, and ∠tilt = 6.0±0.9° with reasonable assumptions for the three other structural parameters. The relatively large uncertainty in these structural parameters results from the large uncertainty in the A rotational constants. These parameters are compared to the corresponding ones in some other peroxides. The quadrupole coupling constants have been obtained and are discussed.     

Étude en ondes millimétriques des variétés isotopiques en 13c et 18o de la molécule de trioxane: Structure de la molécule

The rotational spectra of the molecules (¹³CH₂O)(¹²CH₂O)₂ and (CH₂¹⁸O) (CH₂¹⁶O)₂ have been investigated in the region 30–290 GHz. The rotational constants determined are (MHz):A = 5271.106±0.007, B = 5176.405 ±0.007, C = 2904.376±0.34 for the former, andA = 5267.34±0.3, B = 508I.106±0.3, C = 2872.378± 10 for the latter molecule.The parameter C of the parent molecule (CH₂O)₃ has been determined: 2933.95 ±0.34 MHz. With the value A = B = 5273.258 ±0.002 for the parent molecule the following structural parameters were determined: r(C-O) = 1.4205± 0.005 Å, ∠COC = 109.5±0.5°, ∠OCO = 112±0.5°.     

Ab initio potential energy surfaces for BH+2

Preliminary ab initio calculations for the BH⁺₂ potential surface are presented. The reaction B⁺¹S) + H₂ → BH⁺ (B₂ (B²σ⁺) + H is shown to be most likely to occur for C_2v and near C_2v geometrics where there are avoided crossings between the 1 ¹A₁ and 2 ¹A₁ surfaces and between the 2 ¹A₁ and 3 ¹A₁ surfaces which should facilitate non-adiabatic transitions. Bent geometries are alos preferred for the reaction B⁺(¹S) + H₂ → BH⁺(A²π) + H for which there are avoided crossings in C₂ sysmmetry between surfaces correlating with 1 ¹A₁ and 1 ¹B₂ surfaces.     

Microwave spectrum of dichloroborane (BHCl2)

The microwave spectrum of dichloroborane has been observed and the rotational constants of four isotopic species are determined as follows: A = 46911.09(7), B = 3185.937(10) and C = 2980.425(14) MHz for the normal species, A = 46747.14(8), B = 3099.543(14) and C = 2904.037(14)MHz for BHCl³⁷Cl, A = 49302.05(24), B = 3185.536(32) and C = 2989.368(51) MHz for ¹⁰BHCl₂ and A = 35153.18(9), B = 3186.026(15) and C = 2918.233(11) MHz for BDCl₂. The following complete r_s structure was determined: r_s(BH) = 1.184(2) Å, r_s(BCl) = 1.735(2) Å and ∠ ClBCl = 120.4(2)°. The hyperfine structure due to the two chlorine and one boron nuclei has been analysed.     

Electron scattering differential cross sections for C2H2, C2H4, and C2H6 by gas phase electron diffraction - binding effects

Experimental differential cross sections for 40 keV electrons scattered by C₂H₂, C₂H₄ and C₂H₆ molecules were measured using the gas electron diffraction method in the range of the scattering variable s from s = 1 A^?1 to s = 30 A^?1. The differential cross sections for neon were also measured and compared with calculated differential cross sections to calibrate the diffractograph. Experimental differential cross sections show significant deviations with respect to theoretical differential cross sections calculated from the Debye-Ehrenfest model, mainly in the range of small scattering angles. The observed differences are connected to chemical binding effects. From the experimental data, an estimation of the binding energy was carried out. The deduced values: ?0.58 ± 0.20 au for C₂H₂, ?0.94 ± 0.30 au for C₂H₄ and ?1.23 ± 0.40 au for C₂H₆ are in agreement with those obtained by thermochemical methods.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Observation of X1A1 vinylidene by photoelectron spectroscopy of the C2H2− ion

Photoelectron spectra of the vinylidene anion (C₂H₂^?) show vibrational structure in X¹A₁ vinylidene up 12 kcal/ mol above the vibrational ground state. Analysis yields an EA(C₂H₂$\text{X}$¹ A₁) of 0.47 ± 0.02 eV, and frequencies for the CC stretch and HCH bend. Absence of the ³B₂ state in the photoelectron spectra indicates the ¹A₁-³B₂ splitting in vinylidene is ? 1.7 eV.     

Microwave spectrum, centrifugal distortion, dipole moment and conformation of 2-methyl-1,3-dioxane

Microwave spectrum of 2-methyl-1,3-dioxane has been investigated in the frequency range 8–40 GHz. Rotational a-type and c-type transitions with J≤40 have been identified. Rotational constants A = 4658.122(2) MHz, B = 2503.221(1) MHz, C = 1783.950(1) MHz and centrifugal distortion constants for the ground vibrational state have been found. Dipole moment components μ_a = 1.43 ± 0.01 D, μ_c = 1.15±0.01 D and overall dipole moment μ = 1.84±0.02 D have been determined. The data obtained are in accord with the chair conformation of the molecule having equatorial arrangement of the methyl group. Original Russian Text Copyright ? 2006 by A. Kh. Mamleev, R. V. Galeev, L. N. Gunderova, M. G. Faizullin, and A. A. Shapkin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No.2, pp. 373–375, March–April, 2006.     

Laser induced fluorescence of CH2 (ã1A1) produced in the photodissociation of ketene at 337 nm. The CH2 (ã1A1-X̃3B1)energy separation

The photodissociation of ketene, CH₂CO(X?¹A₁) → CH₂ (ã¹A₁) + CO(X ¹Σ⁺) has been observed at 337 nm, using a pulsed nitrogen laser. The CH₂ (ã ¹A₁) radical has been detected by laser induced fluorescence with a tunable dye laser. A laser excitation spectrum has been obtained from CH₂(ã ¹A₁) over the wavelength interval from 588.9 to 595.6 nm in the Σ ← Π vibronic subband of the CH₂ (ã ¹A₁); υ″ = 0, 0, 0?b? ¹B₁; υ′ = 0, 14, 0) transition. For the CH₂(ã ¹A₁ ; υ′= 0, 0, 0?X? ³B₁; υ′' = 0, 0, 0) energy separation an upper limit of (6.3 ^± 0.8) kcal/mole has been found. The radiative lifetime τ and the rate constant k for the removal of the 0₀₀ rotational level of the Σ(0, 14, 0) vibronic state have been measured directly. The values are τ = (4.2 ^± 0.2) μs and k = (7.4 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1, respectively.     

Microwave spectra of tetrahydroselenophene-α13C, -β13C and molecular ring structure

Microwave spectra of isotopic species α-¹³C and β-¹³C of tetrahydroselenophene molecules have been investigated and rotational constants determined: A = 5608.98 Mc, B = 2819.532 Mc, C = 2022.624 Mc forα-¹³C isotopic species and A = 5695.94 Mc, B = 2770.714 Mc, C = 2009.166 Mc for β-¹³C isotopic species. The r_s-ring structure was found to be Se-C₂ = 1.963 Å, C₂-C₃ = 1.549 Å, C₃-C₄ = 1.527 Å, ∠C₅SeC₂ = 90° 44', ∠SeC₂C₃ = 104° 58', ∠C₂C₃C₄ = 106° 52', the angle of twist = 29° 44'.     

Microwave spectrum of 3-nitrothiophene

The microwave spectrum of 3-nitrothiophene has been studied in the frequency region 26.5–40.0 GHz. The rotational transitions of the ground state and the first six torsionally excited states have been assigned. The ground state rotational constants have been determined to be A_o=4622.61 ± 0.07 MHz, B_o = 1231.751 ± 0.001 MHz and C_o = 973.062 ± 0.001 MHz. The planarity of the molecule has been demonstrated. The first torsional frequency and the barrier to internal rotation of the nitro group have been estimated as 60 cm^?1 and 3.8 kcal/mole, respectively.     

Laser fluorescence spectroscopy and lifetime of the 2B1 (K′ ⪢ 0) electronic state of NO2

Fluorescence of NO₂ excited by HeCd 442 nm laser radiation is found to exhibit a spectrum characteristic of perpendicular transitions from several levels belonging to ²B₁ (K′ ? 0) vibronic states. The lifetime of a level K′ = 4, N′ = 16 ± 1 is 36 μs, substantially greater than lifetimes given previously for K′ = 0 levels of the ²B₁ state. This result supports the mechanism of lifetime lengthening by the Renner interaction of the ²B₁ and ²A₁ components of the linear ²Π_u state.     

The microwave spectrum of the unsymmetrical conformation of 1-chloro-2-methyl propane

The microwave spectrum of 1-chloro-2-methyl propane has been recorded and lines assigned to ³⁵Cl and ³⁷Cl species in the unsymmetrical conformation. The rotational and distortion constants in MHz are: C₄H₉³⁵Cl, A = 7527.05, B = 2146.21, C = 1793.59, Δ_JK = 4.15 × 10^?3, δ_j = ?8.0 × 10^?5; C₄H₉³⁷Cl, A = 7524.40. B = 2091.73, C = 1755.54, Δ_JK = 2.5 × 10^?3, δ_j = 2.0 × 10^?4.     

The microwave spectrum,structure and centrifugal distortion constants of 2-chloroacrylonitrile

The microwave spectrum of 2-chloroacrylonitrile has been studied in the 26.5–40 GHz region. A total of 99 a- and b-type rotational transitions have been measured and assigned for CH₂ =C³⁵Cl(CN),yielding values for the rotational constants (in MHz): A = 6973.27, B = 3148.16, C = 2165.95. For CH₂=C³⁷Cl(CN) a total of 53 transitions have been measured and assigned and the rotational constants obtained are (in MHz): A = 6909.35, B = 3081.17, C = 2127.98. The distortion effects have also been studied and the quartic distortion constants have been evaluated. From the observed hyperfine structure, the chlorine nuclear quadrupole coupling constants have been obtained. The structure of vinyl cyanide and vinyl chloride can be transferred to account remarkably well for the observed rotational constants.     

Magnetic investigation of Er(C2O4) (C2O4)·3H2O

Single crystal susceptibilities of Er(C₂O₄) (C₂O₄H)·3H₂O are reported over the 1.5–20 K interval, and EPR spectra at 4.2 K of Y (C₂O₄) (C₂O₄H·3H₂O doped with Er³⁺ are also reported. The susceptibilities follow the CurieWeiss law, with g_| = 12.97 ± 0.05, g_⊥ = 2.98 ± 0.05, θ_| = ?0.25 ± 0.05 K, and θ_⊥ = ?0.12 ± 0.05 K.     

Microwave spectrum,centrifugal distortion constants,dipole moment and quadrupole coupling constants of pentafluoropyridine

Pentafluoropyridine has been analysed in the frequency range of 8 to 18 GHz at dry ice temperature, using a conventional 100 kHz Stark modulated microwave spectrometer. The rotational constants and centrifugal distortion constants are A = 1481.539 ± 0.003 MHz, B = 1075.348 ± 0.004 MHz and C = 623.101 ± 0.001 MHz; and d_J = ?0.39 ± 0.06 kHz, d_JK = 1.86 ± 0.27 kHz, d_K = 0.70 ± 0.1 kHz, d_EJ = (0.3 ± 0.03) × 10^?6 and d_EK = (?1.5 ± 0.2) × 10^?6. The electric dipole moment has been found to be 0.98 ± 0.08 D and the values of the quadrupole coupling constants are x_aa = 1.94 ± 0.22 MHz, x_bb = ?4.08 ± 0.06 MHz and x_cc = 2.14 ± 0.22 MHz. A simple analysis based on Townes and Dailey theory points to a considerable increase in the π-electron density and excess charge on the nitrogen site.     

Determination of the rate constant for the reaction NH3 + OH → NH2 + H2O

The rate constant for the reaction NH₃ + OH → NH₂ + H₂O was determined by the comparison of the calculated induction period data with experiments by the shock tube technique in the range 1360–1840 K, for NH₃-H₂-O₂-Ar mixtures. The rate constants can be represented by the expression k = 10^12.49±0.04exp[(?1.95±0.15) kcal/,RT] cm³ mol^?1 s^?1.     

Kinetics of the reactions OH (v = O) + NH3 →; H2O + NH2 and OH(v = O) + O3 → HO2 + O2 AT 298°K

The rate constants for the reactions OH(X₂Π, ν = O) + NH₃ → ^k1 H₂O + NH₂ and OH(X²Π, ν = O) + O₃^k2 → HO₂ + O₂ were measured at 298°K by the flash photolysis resonance fluorescence technique. The values of the rate constants thus obtained are K₁ = (4.1 ± 0.6) × 10^?14 and k₂ = (6.5 ± 1.0) × 10^?14 in units of cm³ molecule ^?1 sec¹. The results are discussed in terms of understanding the dynamics of the perturbed stratosphere.