The structure and extinction of nonpremixed methane/nitrous oxide and ethane/nitrous oxide flames

Knowledge of combustion of hydrocarbon fuels with nitrogen-containing oxidizers is a first step in understanding key aspects of combustion of hypergolic and gun propellants. Here an experimental and kinetic-modeling study is carried out to elucidate aspects of nonpremixed combustion of methane (CH₄) and nitrous oxide (N₂O), and ethane (C₂H₆) and N₂O. Experiments are conducted, at a pressure of 1 atm, on flames stabilized between two opposing streams. One stream is a mixture of oxygen (O₂), nitrogen (N₂), and N₂O, and the other a mixture of CH₄ and N₂ or C₂H₆ and N₂. Critical conditions for extinction are measured. Kinetic-modeling studies are performed with the San Diego Mechanism. Experimental data and results of kinetic-modeling show that N₂O inhibits the flame by promoting extinction. Analysis of the flame structure shows that H radicals are produced in the overall chain-branching step 3H₂ + O₂ ? 2H₂O + 2H, in which molecular hydrogen is consumed. Hydrogen is also consumed in the overall step N₂O + H₂ ? N₂ + H₂O where stable products are formed. Inhibition of the flames by N₂O is attributed to competition between these two overall steps.     

Critical conditions for nitrous oxide ignition

The minimum energies of ignition of gaseous nitrous oxide are measured at pressures up to 3 MPa. The minimum pressure at which nitrous oxide burnt out in the reactor completely was 0.5 MPa. It is shown that this pressure depends on the length of the vertically installed cylindrical reactor. At the optimal length, the minimum pressure was as low as 0.3 MPa. The effect of organic lubricants on the ignition energy is discovered. Liquid nitrous oxide failed to be ignited by a flame torch.     

Flame propagation in gaseous nitrous oxide

The characteristics of the propagation of a nitrous oxide decomposition flame in a tube with an internal diameter of 70 mm were measured. It was demonstrated that the pattern of flame propagation and the extent of burnout are determined by the convective motion of the flame kernel because of a very slow burning of nitrous oxide. The laminar flame speed estimated from pressure oscillograms and calculated using thermal theory of flame propagation was found to be ～1 cm/s. The critical diameter of flame quenching in channels were measured to decrease from 10 to 4 mm as the pressure was increased from 15 to 20 atm. Because of the possibility of reignition of the fresh mixture behind the flame arrester by the outflowing combustion products, the channel should be significantly longer than 200 mm.     

The reaction of nitrous oxide with rhodium

A clean rhodium filament at room temperature is highly reactive towards nitrous oxide. The oxygen atom of the N₂O molecule is adsorbed with a sticking probability of 0.45 whilst the nitrogen atoms appear in the gas phase as molecular nitrogen. The room temperature uptake of oxygen is about 5 × 10¹⁴ atom cm^?2 and is independent of nitrous oxide pressure in the range 3.5 × 10^?8 to 1.1 × 10^?6 torr. The adsorption curve is of typical form with an initial region of essentially constant sticking probability. For the first 80% of adsorption at room temperature the shape is satisfactorily accounted for if molecules are able to visit 4–5 adsorption sites whilst held in a weakly-bonded precursor state.     

Decay pathways of superexcited states of nitrous oxide

The ionization and ionic dissociation of the superexcited state of N20 are studied by using electron energy loss spectroscopy and positive ion time-of-flight mass spectroscopy at different momentum transfers; that is, 0 and 0.23 a.u. （atomic unit） . The transitions at 13.8 eV and 14.0 eV are reassigned as 3pπ（000） and 3pσ（000） converging to A^2∑＋, respectively. The competition between the main decay pathways of superexcited states at different momentum transfers is revealed. It is found that 3dσ converging to C^2∑＋ mainly decays into N2O^＋ while 4dσ can decay into both N2^O＋ and NO^＋.     

Bands of nitrous oxide at 5.3 μm

Several bands of nitrous oxide occurring in the region of about 5.3 μm have been measured by using a high resolution vacuum infrared spectrograph. The molecular constants derived from the data have been given along with the basic data.     

Sextic centrifugal distortion constants of ozone

Theoretical expressions for the sextic centrifugal distortion constants of triangular triatomic molecules, as given by Sumberg and Parker, have been evaluated for the ozone molecule. For this calculation, the harmonic frequencies and cubic anharmonic potential constants determined by Barbe, Secroun, and Jouve were used. The calculated distortion constants were compared to complete sets of measured distortion constants recently determined by Maki, and by Barbe et al. Even though the measured constants range over more than four orders of magnitude, we find that the theory reproduces the relative magnitudes and the algebraic signs of the constants quite well. Absolute quantitative agreement is considerably better than order-of-magnitude.     

Dipole moment functions of carbon dioxide and nitrous oxide

The vibrational wavefunctions obtained from the direct numerical diagonalization of the vibrational Hamiltonian matrix are used to compute the matrix elements of transition dipole moments for carbon dioxide and nitrous oxide. The computed matrix elements are found very close to those obtained previously by the contact transformation method. The least-squares fit of the dipole moment derivatives up to the second order has been attempted. It is shown that the values as well as the signs of the second derivatives can be determined if the mechanical anharmonicity contributes considerably to the corresponding combination and/or difference bands. The bands selected for N₂O include the fundamentals, first overtones, binary combination, and difference bands as well as the bands coupled with the above by Fermi resonances. The converged set of the dipole moment derivatives of N₂O gives the computed matrix elements very close to the observed. This also demonstrates the wider applicability of the direct diagonalization method.     

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.     

HNCS分子的光谱常数和非谐振力场的理论研究

采用Gaussian09数据包,以密度泛函理论（B3LYP、B3PW91）和二阶微扰（MP2）方法,分别采用基组6-311+G、6-311++G(2d,2p)、cc-PVNZ(N=T,Q)以及加入弥散函数的高角动量基组aug-cc-PVNZ(N=T,Q)等计算了HNCS分子的光谱常数和非谐振力场。结果表明：B3LYP、B3PW91和MP2计算的结果与实验结果都比较接近;当基组由VTZ增大到VQZ或加弥散函数对结果的影响均不明显;其中B3PW91\cc-PVTZ的各项计算结果相对于其他计算结果更接近实验值。通过计算,可以在前人基础上进一步预测HNCS分子其它的光谱常数（如:非谐性常数、科里奥利耦合常数等）。     

HNCS分子的光谱常数和非谐振力场的理论研究

采用Gaussian09数据包,以密度泛函理论(B3LYP、B3PW91)和二阶微扰(MP2)方法,分别采用基组6-311+G、6-311++G(2d,2p)、cc-PVNZ(N=T,Q)以及加入弥散函数的高角动量基组aug-ccPVNZ(N=T,Q)等计算了异磺氰酸(HNCS)分子的光谱常数和非谐振力场.结果表明:B3LYP、B3PW91和MP2计算的结果与实验结果都比较接近;当基组由VTZ增大到VQZ或加弥散函数对结果的影响均不明显;其中B3PW91/cc-PVTZ的各项计算结果相对于其他计算结果更接近实验值.通过计算,可以在前人基础上进一步预测HNCS分子其它的光谱常数(如:非谐性常数、科里奥利耦合常数等).     

Anharmonic force field of acetylene

The harmonic and anharmonic force field of acetylene has been determined in a least-squares calculation from recently determined data on the spectroscopic constants of various isotopic species (including the vibrational l-doubling constant). A general quadratic and cubic force field was used, but a constrained quartic force field containing only 8 of the 23 possible quartic constants. The results are discussed and compared with earlier work.     

Sextic centrifugal distortion constants of polyatomic molecules

Detailed expressions, in terms of fundamental molecular parameters, are given for the sextic centrifugal distortion constants for a general polyatomic molecule. The calculation of these expressions is based on the Watson molecular vibrational-rotational hamiltonian using third and fourth-order ordinary perturbation theory. Numerical examples are given for the H₂S, SO₂ and NH₃ molecules. The calculated and observed sextic constants for these molecules are in good agreement.     

六次非简谐振子的多尺度微扰理论

应用多尺度微扰理论, 对于弱耦合常数的六次非简谐振子得到了其运动方程的经典和量子情况下的一阶解. 与Taylor级数解不同的是, 无论是在经典和量子解中频率移动出现在各阶表达式中, 因此多尺度微扰理论是优于Taylor级数解的一种处理弱耦合常数非简谐振动的近似方法.     

Emissivity and band-model parameters for infrared bands of nitrous oxide

Narrow band-model parameters S/d, γ_N/d and B have been obtained experimentally for the v₃, v₁ and 2v₂ bands of N₂O in the temperature range from 200°K to 500°K. The exponential-wide band-model parameters have been determined for all of the contributing bands and have been found to differ greatly from the values of Tien et al. Data of revised total gas emissivities are presented.     

Anharmonic force field for methanol

An ab initio quartic anharmonic force field for methanol has been calculated at the equilibrium position using the CCSD(T) method for the structure and the harmonic potential energy surface, and the MP4(SDQ) method for the anharmonic part of the surface. A triple zeta basis set was employed with symmetrized curvilinear internal valence coordinates in all calculations. The internal coordinate force field constants have been transformed into force constants in the dimensionless normal coordinate representation for various isotopomers. Vibrational term values for CH₃OH, CH₃OD, CD₃OH, and CD₃OD have been obtained using second order perturbation theory. Particular care has been devoted to the inclusion of Fermi resonance interactions between different vibrational states. A good accuracy has been achieved in the calculation of the fundamentals for all the isotopomers, the mean absolute error being 5.8 cm^?1.     

Anharmonic force field for FCP

It is shown that, whereas a simple harmonic force field suggests that the FC stretching constant exceeds that for CP, a fuller anharmonic treatment suggests values of 806 and 946 N m^?1, respectively. Equilibrium bond lengths are 127.17 and 154.81 pm respectively.     

Uniqueness of methyl fluoride force field

The uniqueness of the general harmonic force field of methyl fluoride is analyzed. The analysis is applicable to other methyl halides as well. Through the compliance scheme, it is seen that by supplementing the data employed by Aldous and Mills (i.e., vibrational frequencies ω_i, Coriolis coupling constants ζ_i and the centrifugal stretching constants D_J, D_JK of CH₃F and CD₃F molecules), with the frequencies of A′ or A″ species of either CH₂DF or CD₂HF, the force field is uniquely determined. The addition of any other extra data including the ¹²CH₃F¹³CH₃F isotopic shifts only makes the determination of the force field parameters more precise.