Sextic force field of nitrous oxide

The sextic force field in the curvilinear internal coordinates has been studied for the nitrous oxide molecule from the spectroscopic data of ¹⁴N₂¹⁶O, ¹⁴N¹⁵N¹⁶O, and ¹⁵N¹⁴N¹⁶O. The bands below 6600 cm⁻¹ have been used. The force constants in the internal coordinates are converted to those in dimensionless normal coordinates by two successive transformations. The vibration Hamiltonian matrix for each symmetry species of a given isotopic species has been constructed from the harmonic oscillator basis functions, and it is then diagonalized numerically to give the vibrational energy levels and the wavefunctions. The latter have been used for the evaluation of ratational constants. The least-squares refinement has been very successful in the present study, and it is shown that the general quartic force field supplemented by the quintic and sextic stretching diagonal force constants estimated from the Morse function, provided that the terms up to sextic are kept in the dimensionless normal coordinate space, well reproduces the spectroscopic constants such as the vibrational levels, rotational constants, l-type doubling constants, and centrifugal distortion constants. The spectroscopic constants of the isotopic molecules which are excluded from the refinement process are also in good agreement with the computed ones. The bond dissociation energies of the NN and NO bonds estimated from the present results have been critically examined.     

The high resolution infrared spectrum of the 2ν2 + ν3 and ν1 + ν2 + ν3 bands of 14N16O2: Vibration and vibration-rotation constants of the electronic ground state of 14N16O2

The A-type bands, 2ν₂ + ν₃ and ν₁ + ν₂ + ν₃, with band centers at 3092 and 3638 cm^?1, respectively, of ¹⁴N¹⁶O₂ have been measured with resolution of 0.03 cm^?1 or better. Spectroscopic constants have been derived for the upper states of both bands. Infrared determined band constants have been combined with laser-excited resonance fluorescence data to obtain a set of vibration and vibration-rotation constants for the ground state of ¹⁴N¹⁶O₂.     

The 2ν1 + ν3 and 3ν3 bands of 14N16O2

The spectra of the 2ν₁ + ν₃ and 3ν₃ bands of ¹⁴N¹⁶O₂ have been recorded by means of high-resolution Fourier transform spectroscopy and have been extensively analyzed. The (2 0 1) and (0 0 3) rotational levels deduced from the analysis have been reproduced within the experimental uncertainty using a Hamiltonian which takes into account the Coriolis interaction coupling the vibrational states of the diads {(2 2 0), (2 0 1)} and {(0 2 2), (0 0 3)}. Finally, precise sets of vibrational energies, and spin-rotation, rotational, and coupling constants have been derived for these vibrational states.     

Dissociation equilibrium of dinitrogen tetroxide in organic solvents: An electron paramagnetic resonance measurement

The dissociation equilibrium of N₂O₄−NO₂ has been measured in hexane, carbon tetrachloride and chloroform at different temperatures. The equilibrium constants at 298.15 K (25°C),K _m (molality basis), are 3.5·10⁻⁵ in hexane, 5.9·10⁻⁶ in carbon tetrachloride and 5.3·10⁻⁶ in chloroform. The EPR technique has been used to quantify the NO₂ radical. These data are compared with gas-phase and solution data of previous reports. The applicability of Hildebrand and Scatchard theory of solutions is also discussed and some thermodynamic properties are deduced, such as Henry’s N₂O₄ and NO₂ constants in different solvents.     

The rotational a-type sepctra of 15N-labeled diazirine,H2CN2

The rotational a-type spectra of isotopically enriched diazirine isotopomers, H₂¹²C¹⁴N¹⁵N and H₂¹²C¹⁵N₂, have been recorded in the region between 8 and 300 GHZ; the latter isotopomer has been observed for the first time. Using Watson's A-reduced Hamiltonian, the rotational constants and the quartic and some sextic centrifugal distortion constants have been determined for the ground vibrational states.     

The microwave spectrum of cyanophosphaacetylene, H2PCCCN

The a type transitions of the microwave rotational spectra of cyanophosphaacetylene, H₂PCCCN, have been investigated in the frequency region between 5 and 26.5 GHz by Fourier transformation microwave (FTMW) spectroscopy. Rotational, centrifugal distortion and ¹⁴N nuclear quadrupole coupling constants have been determined. Density functional theory level ab initio calculations were performed to predict the molecular constants, and the predicted values are in good agreement with our experimentally determined results. The ¹³C and ¹⁵N isotopomer transitions were also observed. The derived r₀ structure is quite comparable to the calculated H₂PCCCN equilibrium geometry.     

Analysis of the ν3 band of NO2

The rotational structure of the ν₃ fundamental of ¹⁴N¹⁶O₂ has been recorded by employing a vacuum grating infrared spectrograph. The analysis has led to the assignment of over 500 R- and P-branch transitions in the spectral region 1562–1650 cm⁻¹. Molecular constants for the upper state, 001, have been presented. No Q-branch transitions were used in the evaluation of these constants. The presently obtained and the band center ν₀ = 1616.846 cm⁻¹ differ significantly from previous determinations. Spin splitting was observed but no information was extracted about upper state spin splitting parameters.     

The far infrared spectrum of 14N16O2

High resolution Fourier transform spectra in the 8–200 cm^-1 spectral region have been used to analyse the pure rotation spectrum of nitrogen dioxide. In this way, the spin rotation levels of the (000) state were accurately measured for K_a up to 14 and N up to 54. Using a hamiltonian which takes the spin-rotation and the hyperfine operators explicitly into account, it has been possible to derive a complete set of molecular parameters (rotational, spin-rotation and hyperfine constants) for the (000) state of ¹⁴N¹⁶O₂ from these experimental data and from the available microwave measurements. Numerous perturbations due to the hyperfine Fermi contact operator were analysed as well as a local resonance [42 0 42, J = 41·5] ? [41 2 40, J = 41·5] due to the electron spin-rotation interaction. Finally, a synthetic spectrum of the (000) ← (000) band of ¹⁴N¹⁶O₂ including all hyperfine transitions has been computed, covering the 0–235 cm^-1 spectral region.     

N2O+离子A2Σ+电子态高振动能级的转动结构分析

利用一束波长为36055nm的激光,通过(3+1)共振多光子电离方法制备纯净的且处于X²Π_1/2,3/2(000)态的N₂O⁺离子,用另一束激光激发所制备的离子到第一电子激发态A²Σ⁺的不同振动能级,然后解离,通过检测解离碎片NO⁺强度随光解光波长的变化,得到了转动分辨的N₂ 关键词： 2O⁺离子A²Σ⁺电子态')" href="#">N₂O⁺离子A²Σ⁺电子态 共振增强多光子电离 光解碎片激发光谱 光谱常数     

Theoretical studies of three-dimensional potential energy surfaces using neural networks and rotational spectra of the Ar–N2 complex

ABSTRACT

A new three-dimensional potential energy surface (PES) of the Ar–N₂ van der Waals complex is constructed using the neural network method based on ab initio data points at the CCSD(T) level. The aug-cc-pVQZ basis set is employed for all atoms with midbond functions. The vibrationally averaged PES V₀₀ is characterised by a global T-shaped minimum which occurs at R = 3.715 Å, θ = 90.0° with a well depth of 98.779 cm^?1. Based on our three-dimensional PES, bound-state calculations are performed for three isotopomers of Ar–¹⁴N₂, Ar–¹⁵N₂, and Ar–¹⁴N¹⁵N, and several intermolecular vibrational states are assigned by analysing the wavefunctions. Moreover, the averaged structural parameters are calculated and the pure rotational transition frequencies with J = 0--6 are predicted. The spectroscopic constants are determined by fitting the rotational energy levels. The theoretical results are in good agreement with experimental data and this work gives more accurate results than those determined previously for the Ar–N₂ complex.     

Nitrogen-15 Fractionation in the Thermal Decomposition of Nitrous Oxide of Natural Isotopic Composition

Abstract

The ¹⁵N fractionation in the thermal decompostion of nitrous oxide (N₂O) of natural isotopic composition has been investigated in quartz reaction vessel in the temperature interval 888–1073K. The formulas relating the observed experimentally ¹⁵N fractionations with the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p for ¹⁴N¹⁵N¹⁶O, and secondary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_s for ¹⁵N¹⁴N¹⁶O, have been derived. The experimentally estimated ¹⁵N kinetic isotope effects have been compared with the primary and secondary ¹⁵N kinetic isotope effects calculated with the absolute rate theory formulations applied to linear three atom molecules. A good agreement was found for the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p, in the temperature interval 888–1007K. But at 1073K the decompositions of N₂O, accompanied by NO (nitric oxide) formation proceed with a twice times smaller primary kinetic isotope effect, (k ¹⁴/k ¹⁵)_p of 1.0251 ± 0.0009, only, suggesting the nonlinear transition state structures with participation of the fourth external atom at high temperature decompositions of nitrous oxide. The nitrogen isotope effects determined in this study correlate well with nitrogen isotope fractionations observed in the natural biological, earth and atmospheric processes.     

Magnetic Moment of the 3/2− Ground State of 185W

Nuclear magnetic resonance measurement have been performed for ¹⁸⁵W oriented at 8 mK in an Fe host. The magnetic hyperfine splitting frequency at an external magnetic field of 0.1 T was determined to be 196.6(2) MHz. With the known hyperfine field of B _hf = −71.4(18) T, the nuclear magnetic moment of ¹⁸⁵W is deduced as μ(¹⁸⁵W) = +0.543(14) μ_N.     

A re-examination of the I.R. spectrum of dinitrogen trioxide

Assuming a planar geometry of C _s symmetry and using a Urey-Bradley potential field, the force constants of dinitrogen trioxide have been re-determined within the formalism of Wilson's G-F matrix method. The outcome of the present investigation suggests a new set of force constants some of which are drastically (～ 50 per cent) different than those previously reported. Furthermore, since the i.r. frequencies used in the present investigation were obtained both in the solid state and at low temperatures, the mean amplitudes of thermal vibrations of both ¹⁴N₂O₃ and ¹⁵N₂O₃ are given at 77°k. Finally, it is suggested that more isotopic i.r. data is necessary to ascertain unequivocably the geometry of dinitrogen trioxide.     

Vibration-rotation bands of nitrous oxide: 4.1 micron region

The infrared spectrum of nitrous oxide has been measured and analyzed from 2265 cm^?1 to 2615 cm^?1. Newly refined effective rotational constants for twenty-one vibrational states of ¹⁴N₂O, three vibrational states each of ¹⁴N₂¹⁸O and ¹⁵N¹⁴N¹⁶O, two states of ¹⁴N¹⁵N¹⁶O and one state of ¹⁴N₂¹⁷O have been calculated.The most interesting features observed are two Δ-Σ “forbidden” bands, 04^2c0-00⁰0 and 12^2c0-00⁰0. These bands occur because of Coriolis interaction between unperturbed vibrational states having l = 0 and l = 2.     

Vibration-rotation bands of 15N216O14N218O

The infrared spectrum of 64 bands of the isotopic species ¹⁵N₂¹⁶O of nitrous oxide and of 37 bands of ¹⁴N₂¹⁸O have been analyzed. The studied spectral range extends from 1750 to 6000 cm^?1 for ¹⁵N₂¹⁶O and from 1750 to 3100 cm^?1 for ¹⁴N₂¹⁸O. The effective rotational constants are given for 44 levels of ¹⁵N₂¹⁶O comprising 21Σ, 12Π, 7Δ, 4Φ levels and also for 29 levels of ¹⁴N₂¹⁸O comprising 13Σ, 7Π, 6Δ, 3Φ levels. Thirty-one levels (20Σ, 11Π) of the following isotopic species have also been studied: ¹⁵N₂¹⁷O, ¹⁵N₂¹⁸O, ¹⁴N¹⁵N¹⁸O, ¹⁵N¹⁴N¹⁸O, ¹⁴N₂¹⁷O. In ¹⁵N₂¹⁶O a local Coriolis resonance affects the 10⁰1 level. The “forbidden” Δ-Σ transition 12^2c0-00⁰0 is observed in the spectrum of ¹⁵N₂¹⁶O. The equilibrium values for the internuclear distances have been calculated.     

Ab initio calculation of force constants for the linear molecules HCN,FCN, (CN)2 and the ion N2F+

Force constants have been calculated from ab initio Hartree-Fock wave-functions by the force method, using 7s3p/1 and 5s2p/1 gaussian basis sets for HCN, FCN, C₂N₂ and FN₂ ⁺. Agreement of the quadratic and some cubic force constants with experiment is good for HCN and FCN. The influence of anharmonicity upon the l-type doubling constant of FCN is estimated. Both the experimental l-type doubling constant and the ab initio calculations indicate that the quadratic stretch, stretch coupling constant is positive in FCN, contrary to recent results of Wang and Overend, obtained from the Anderson potential function. There is good agreement for the CN, C′N′ coupling in C₂N₂ but the calculated CN, CC coupling, although positive, is much lower than in two recent experimental force fields. The calculated FN, NN coupling in FN₂ ⁺ is small and positive. The predicted geometry of FN₂ ⁺ is r _NF = 1·28 Å, r _NN = 1·10₅ Å. The validity of the Anderson potential function is discussed.     

High-Resolution IR Spectroscopy of the N2O-H2O and N2O-D2O van der Waals Complexes

We report high-resolution infrared vibrational-rotational spectra of the weakly bound complexes N₂O-H₂O and N₂O-D₂O in the higher frequency N₂O stretching mode region (ν₃=2223.756693(124) cm⁻¹). The measurements were carried out using a free jet expansion in combination with a lead salt diode laser spectrometer. Rotational constants, quartic centrifugal distortion constants, and band origins have been derived for both isotopomers. The geometrical structure is determined using isotopic substitution. The deduced structure shows evidence for a second hydrogen bond interaction within the complex. The nonrigidity of the complexes gives rise to an internal rotation of the water molecule around its own C_2v symmetry axis. For N₂O-H₂O, a tunneling splitting arising from this internal motion has been observed in the spectra. According to symmetry considerations, the observed splitting in the spectrum of N₂O-H₂O corresponds to the difference between the tunneling frequencies in the ground and vibrationally excited states.     

High‐resolution stimulated Raman study of the first vibrational hot band of 14N2. Separate observation of the spectra of the ortho and para species.

We present high‐resolution stimulated Raman spectra of the first hot band of nitrogen, ¹⁴N₂, obtained under conditions of low sample pressure and temperature. The use of a Raman optical pumping system allowed us to transfer a significant amount of population to the v = 1 vibrational state, which made possible the observation of the aforementioned hot band with good S/N ratio without resorting to the use of high temperatures or pressures. This has resulted in a more precise and accurate determination of the peak positions than previously existing ones, which in turn has yielded improved values for the molecular constants obtained from the analysis. The rotational selectivity of the pumping process (only one rotational state is initially populated in v = 1), coupled with the negligible probability of nuclear spin interconversion in the time frame of the experiment, has allowed us to observe the hot band spectra of the ortho and para species of ¹⁴N₂ separately. Copyright © 2013 John Wiley & Sons, Ltd.     

Microwave spectra and structure of an isoxazole-water complex

The rotational spectrum of a hydrogen-bonded isoxazole-water complex has been measured between 6–18 GHz with a pulsed nozzle Fourier transform microwave spectrometer. In addition to isoxazole-H₂O, the complexes with HDO and D₂O as well as isoxazole-¹⁵ N-H₂O have been investigated in order to determine the structure of the complex. Rotational constants, quartic centrifugal distortion constants and quadrupole coupling constants, where applicable, have been fitted to the measured transition frequencies of the isotopomers. Structural data, which have been deduced from the planar moments of inertia and the quadrupole coupling constants of the isotopomers, have established conclusively that water binds to nitrogen in the ring plane of isoxazole. Ab initio calculations have revealed that complexes with a hydrogen-bond to nitrogen or to oxygen are both stable. The complex with water attached to nitrogen has been found to be more strongly bound than that with water attached to oxygen. Small splittings of the rotational transitions of the two complexes with H₂O have been interpreted as being the result of an internal rotation of water with respect to isoxazole.     

Development of a field-deployable method for simultaneous,real-time measurements of the four most abundant N2O isotopocules*

Understanding and quantifying the biogeochemical cycle of N₂O is essential to develop effective N₂O emission mitigation strategies. This study presents a novel, fully automated measurement technique that allows simultaneous, high-precision quantification of the four main N₂O isotopocules (¹⁴N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁴N¹⁴N¹⁸O) in ambient air. The instrumentation consists of a trace gas extractor (TREX) coupled to a quantum cascade laser absorption spectrometer, designed for autonomous operation at remote measurement sites. The main advantages this system has over its predecessors are a compact spectrometer design with improved temperature control and a more compact and powerful TREX device. The adopted TREX device enhances the flexibility of the preconcentration technique for higher adsorption volumes to target rare isotope species and lower adsorption temperatures for highly volatile substances. All system components have been integrated into a standardized instrument rack to improve portability and accessibility for maintenance. With an average sampling frequency of approximately 1 h^–1, this instrumentation achieves a repeatability of 0.09, 0.13, 0.17 and 0.12?‰ for δ¹⁵N^α, δ¹⁵N^β, δ¹⁸O and site preference of N₂O, respectively, for pressurized ambient air. The repeatability for N₂O mole fraction measurements is better than 1 ppb (parts per billion, 10^–9 moles per mole of dry air).