On the determination of the potential functions of H<Subscript>2</Subscript>Co,PH<Subscript>3</Subscript>, and CH<Subscript>4</Subscript> molecules based on experimental data

In the present work, a method of determining multidimensional potential surfaces of polyatomic molecules is suggested. The method is based on the use of high-accuracy data on the vibrational-rotational band centers and results of vibrational-rotational theory. Results of application of the method to the CH ₄, PH₃, AsH₃, and H ₂CO molecules are presented. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 58–63, February, 2008.     

Forbidden vibrational-rotational transitions and Herman-Wallis factors in fundamental IR bands of symmetric-top molecules

Within the theory of coupled schemes of ordering of vibrational-rotational interactions, the operator of the effective dipole moment of single-quantum vibrational transitions is represented in the form of an infinite series in vibrational (normal coordinates and conjugate momenta) or rotational variables (components of the total angular momentum). Mechanisms of activation of infrared-inactive totally symmetric vibrations in molecules of the D _2a , D _3h , C _3h , D _n (n ≥ 3), S ₄, T, T _a , and O symmetries and forbidden vibrational-rotational transitions in IR bands of active vibrations have been studied. The group-theoretic analysis of tensor parameters in higher-order effective dipole moments of single-quantum vibrational transitions in axially symmetric molecules has been performed. The strengths of allowed transitions and forbidden transitions in fundamental and hot IR bands of axially symmetric molecules are calculated with allowance for the Herman-Wallis factors. For effective dipole moments of multiquantum transitions in molecules, models are developed in the form of infinite series in rotational variables and in the form of Padé approximants.     

Effect of the Coriolis interaction on the average nuclear separation in nonlinear XY2 molecules

The average nuclear separations are calculated for XY₂ molecules by means of the total vibrational-rotational wave function obtained by a method different from that developed by Nielsen and Amat. A small dimensionless parameter is introduced for an order-of-magnitude estimate of the vibrational-rotational interaction. Terms due to the Coriolis interaction are singled out.Translated from Izvestiya VUZ. Fizika, No. 4, pp. 30–34, April, 1970.     

Semirigid vibrating rotor target calculation for reaction O(<Superscript>3</Superscript>P)+CH<Subscript>4</Subscript>→CH<Subscript>3</Subscript>+OH

The time-dependent quantum dynamics calculation for reaction O(³P)+CH₄ →CH₃+OH is made, using of the semirigid vibrating rotor target (SVRT) model and the time-dependent wave packet (TDWP) method. The corresponding reaction probabilities of different initial states are provided. From the calculation of initial rovibrational statej=0,v=0, 1, we can see that the excitation of the H-CH₃ stretching vibration gives significant enhancement of reaction probability and the reaction threshold decreases dramatically with the enhancement of the vibrating excitation, which indicates that the vibrating energy of reagent molecules contributes a lot to the molecular collision. As for the calculation of reaction probability of statev=0,j=0,1,2,3, the results show that the reaction probability rises significantly with the enhancement of rotational quantum numberj while the reaction threshold has no changes. The spatial steric effect of the title reaction is studied and analyzed too after the calculation of reaction probability of statesj=5,k=0–2,n=0 andj=5,k=2,n=0–2 is made.     

Understanding halogen‐substituent assistance in H‐atom abstraction‐based reactions of CHCl•− with CH4 − nXn (X = H,F, Cl; n = 0–3)

The effect of halogen‐substituent on hydrogen abstraction mechanisms was studied by applying density functional theory functional calculations to the gas‐phase reactions between CHCl^?? and CH_{4 ? n}X_n (X = H, F, Cl; n = 0–3), and it is found that a heavier X substituent in the substrate results in a greater stabilization of corresponding complex, a lower activation energy, a faster H‐abstraction reaction, and greater exothermicity. However, CH₄– reaction is more reactive than CH₃F– reaction under the same condition because of dominant π‐donation from the electronegative F atom. We also explored the reactivity difference for the seven reactions in terms of factors derived from bond order, second‐order perturbative energy, and activation strain model analysis. The rate constants are evaluated over a wide temperature range of 298–1000 K by the conventional transition state theory. Copyright © 2014 John Wiley & Sons, Ltd.     

Irreducible tensor operators and operations over them in the theory of molecular spectra

The explicit shape of symmetrized powers of three-dimensional representations of the groups Td and Oh is found in general form. Equations are obtained for calculating the vibrational commutators and matrix elements of irreducible tensor operators. Programs have been developed (in the C and FORTRAN languages) to remove the multiple-valued property of the vibrational-rotational Hamiltonian of spherical top molecules (CH₄, SiH₄, GeH₄, SF₆, and so on).Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 16–25, March, 1993.     

On the Determination of the Absolute Intensities of Vibrational-Rotational Lines of XY3 Molecules with C 3v Symmetry

Analytical formulas are derived that describe the dependences of the transition probabilities in vibrational-rotational spectra of XY₃-type molecules with C _3v symmetry on the rotational quantum numbers.     

Lifetimes of high Rydberg states of methyl halides

The lifetimes of high Rydberg states of the methyl halides CH₃I, CH₃Br and CH₃Cl have been studied. A pulsed dye laser tuned near half the ionization energy was used, with preprogrammed field pulses, and the high Rydberg states of the compounds in selected ranges of n values were ionized after a variable delay. Plots of the electron signal versus delay yielded information about the Rydberg state lifetime. The clearest trend was found for around n = 120–160: the lifetimes of the states decreased by more than an order of magnitude from CH₃I (τ ≈12.3 μs) through CH₃Br to CH₃C1. Within the range studied, the theoretically predicted increase in lifetimes (n ⁵ or n ³) was not found, and in fact the highest group of states studied (with n > 215) exhibited for all three compounds relatively short lifetimes (≈2-3 μs), possibly due to collisional processes.     

Polarization Modulation Effects in Infrared–Infrared Four-Level Double Resonance inCH3F andNH3

The elements of the Jones matrices for an optically pumped sample have been derived and used to predict four-level double resonance absorption coefficients that are functions of the velocity component of the molecules in the direction of the pump beam for different polarizations of the probe beam. When a saturating pump and weak probe are used in four-level double resonance experiments under population modulation conditions, these absorption coefficients are found to depend only on the first three statistical tensor ranks:n= 0 (population), 1 (orientation), and 2 (alignment). It is also found that for polarization modulation experiments with plane-polarized radiation, the absorption coefficient depends only on the alignment of them-state populations. Similarly, for polarization modulation with circularly polarized radiation, the absorption coefficient depends only on the orientation. The theory was used to interpret double-resonance polarization modulation experiments in¹³CH₃F and¹⁵NH₃in order to examine the effects of collisions on the initial anisotropy of the projection ofJon a space-fixedZaxis. The four-level double-resonance lineshapes were fit by least squares to absorption coefficients predicted by the theory. The collisional effects were modeled by a sum of Keilson–Storer collision kernels. The results of the fits were much improved when the value of the effective rate constant for the transfer of then= 0 tensor from the upper level of the pump to the lower level of the probe was larger than the values of the effective rate constants for the transfer of then= 1 and 2 populations. The best ratio of the rate constant forn> 0 to that forn= 0 is about 2/3 for¹³CH₃F and 1/3 for¹⁵NH₃. Additional analysis of the lineshapes showed the importance of long-range dipole–dipole interactions, elastic realignment and reorientation, and V–V mechanisms for collision-induced rotational energy transfer in¹³CH₃F and¹⁵NH₃.     

Semiclassical theory of vibrational,rotational and translational energy exchange in collisions of polyatomic molecules

We derive a theory of inter- and intramolecular transfer of vibrational, rotational and translational energy in collisions of polyatomic molecules, in the case that only short range forces are important. Normal mode vibrations of molecules are treated quantum mechanically whereas translations and rotations are assumed to be classical degrees of freedom. We are able to show that, in case of short range forces, the energy exchange in binary collisions is essentially governed by an effective mass which is given by an algebraic function of the usual reduced mass and moments of inertia and depends also on the relative orientation of the two molecules. As an application of the theory, we calculated the probabilities for collision-induced 1 →0 transitions of the v ₃ mode in pure CH₃I, CH₃Br and CH₃Cl gases. The calculated values are close to the experimental vibrational deactivation probabilities.     

Use of a two-sequential radical reaction scheme to rationalise the high-oxidation-state carbene species detected under confinement conditions for the interactions Fe(5D) + CH4−n Fn (n = 2−4)

Results obtained from CASSCF–MRMP2 calculations are used to explain the carbene products observed under matrix conditions for the interactions Fe(⁵D) + CH_4–nF_n (n = 2–4) in terms of two sequential reactions involving the radical species ·FeF + CH_4–nF_n–1. For the CH₂F₂ and CHF₃ molecules, the first reaction leads to the radical fragments ·FeF + CH₂F (or ·CHF₂). As these species remain trapped in the matrix, they can recombine themselves to form the inserted complex CH₂F–Fe–F (or CHF₂–Fe–F). The carbene H₂C = FeF₂ (or HFC = FeF₂) is reached from the inserted structure by α-migration of an additional fluorine atom to the metal centre. The rebounding reactions can take place along both the quintuplet and triplet asymptotes varying only in the spin of the non-metal fragment. This model explains the triplet compound H₂C=FeF₂ detected for the interaction Fe + CH₂F₂ and allows theoretically assigning as quintuplet the complex HFC=FeF₂ observed for the reaction Fe + CHF₃.     

Calculation of vibrational spectra and force and vibrational-rotational constants of germanium halides of the type GeHnX4−n (X=F,Cl, Br,I; n=0 to 2)

Calculations are made of the frequencies, the form of the normal vibrations, and the constants of the potential energy of displacements of atoms during normal vibrations of germanium halides of the type GeH_nX_4–n (X=F, Cl, Br, I; n=0 to 2) and their deuterium replacements. For displacements of atoms during normal vibrations a calculation is made of the constants of vibrational-rotational interaction in the molecules GeHX₃ and GeX₄. The validity of the calculation is confirmed by the way in which the sum rule for the - and -constants is fulfilled. The mean-square amplitudes are calculated for tetrahedral molecules GeX₄ (X=F, Cl, Br, I). An analysis is given of the strong field of germanium halides GeH_nX_4–n in connection with properties of the structure of the Ge-halide bond.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 54–58, September, 1973.     

Initiation of combustion of a methane-air mixture in a supersonic flow behind a shock wave during laser excitation of O<Subscript>2</Subscript> molecules

The possibility of initiating detonation of CH₄ + air in a supersonic flow behind an oblique shock wave under the exposure of the mixture to laser radiation with wavelengths λ_I=1.268 μm and 762 nm is analyzed. It is shown that this irradiation leads to excitation of O₂ molecules to the a ¹Δ_g and b ¹Σ _g ⁺ states, which intensifies the chain mechanism of combustion of CH₄/O₂ (air) mixtures. Even for a small value of the laser radiation energy absorbed by an O₂ molecule (∼0.05–0.1 eV), detonation mode of combustion in a poorly inflammable mixture such as CH₄/air can be realized at a distance of only 1 m from the primary shock wave front for relatively small values of temperature (∼1100 K) behind the front under atmospheric pressure.     

Intracluster electron transfer from a metal atom/cluster followed by anionic oligomerization of vinyl molecules

Intracluster electron transfer and oligomerization reaction were investigated by mass spectrometry of clusters of alkali metal atom (M) with acrylonitrile (AN; CH₂=CHCN). In the photoionization mass spectra of M(AN)_n, magic numbers were clearly observed at n = 3k (k = 1-4 for M = Na and K, k = 1 for M = Li). The results of photodissociation of neutral K(AN)_n indicate that the n = 3 cluster has an anomalous stability relative to other sizes of clusters. The C=C bond in vinyl molecules is also found to be necessary to form the magic numbers by measuring the photoionization mass spectrum of K atom with propionitrile. These results strongly support the intracluster anionic oligomerization reaction initiated by electron transfer from the alkali atom. The quantum chemical calculations have revealed that the evaporation induced by excess energy generated by intracluster oligomerization is important to form the magic numbers in the present clusters. Received 29 November 2000     

On the ‘expanded local mode’ approach applied to the methane molecule: isotopic substitutions CH3D ←CH4 and CHD3 ←CH4

Operator perturbation theory and the symmetry properties of the axially symmetric XYZ₃ (C_3v) type molecules are used for the determination of the spectroscopic parameters in the form of functions of structural parameters and parameters of the intramolecular potential function. Several relations between sets of spectroscopic parameters of these molecules are obtained. The ‘expanded local mode’ model and the general isotopic substitution theory are used to estimate the relations between spectroscopic parameters of CH₃D and CHD₃, on one hand, and with the T_d symmetric isotopic species, CH₄, on the other hand. Test calculations with the isotopic relations show that even without including prior information about the CH₃D and CHD₃ species, numerical results of calculations are in a good agreement both with experimental data and with results of ab initio calculations.     

Effect of buffer gas on the generation of eye-safe 1.54 μm radiation using the stimulated Raman scattering technique in CH4

Experimental results on the generation of 1.54 μm eye-safe radiation in pure CH₄, CH₄:He and CH₄:Ar mixtures pumped by the fundamental of an Nd:YAG laser, using the stimulated Raman scattering (SRS) technique, are described. A decrease in the energy conversion efficiency and degradation in the beam quality of S₁ was observed in pure CH₄ at high pump energies. This problem was overcome in CH₄:He and CH₄:Ar mixtures. Compared with the first Stokes (1.54 μm) energy conversion efficiency in pure CH₄, at a pump energy of 126 mJ, an enhancement of 50% in energy conversion efficiency was observed in the CH₄:Ar mixture (60% argon concentration) and as much as 100% in the CH₄:He mixture (60% helium concentration). The use of these buffer gas mixtures improved the spatial beam quality of the Stokes radiation considerably and also resulted in raising the pump threshold for optical breakdown of the Raman gain medium.     

355 nm激光光电离甲醛飞行时间质谱的研究

利用脉宽为5 ns脉冲Nd: YAG 355 nm激光在功率密度为10¹¹–10¹² W/cm²条件下实现了甲醛含水团簇多光子电离, 并用飞行时间质谱对其电离产物和电离过程进行了研究. 实验中观测到了甲醛的质子化团簇系列 (CH₂O)_nH⁺(n=1–4), 甲醛的去质子化团簇系列(CH₂O)_nCHO⁺ (n=1–3), 以及两个起源于H₂CO去质子和质子化的含水团簇系列HCO⁺(H₂O)_n(n=1,3,5)和H₃CO⁺(H₂O)_n(n=1,3,5), 并对其中的一些团簇结构构型进行了猜测. 研究在不同的激光功率密度下甲醛团簇质谱峰的变换情况, 当激光密度达到9.3× 10¹¹ W/cm², 开始出现CH₂O和H₂O本体及其光致碎片的信号, 但对应的各质量峰没有明显地分辨开, 而是以包络的形式出现, 这是激光电离产生高能离子释放的一种表现, 提出认等离子体动力学鞘层加速机制(模型)来解释高能离子形成的物理机制. 关键词： 甲醛 团簇 飞行时间质谱 激光电离     

Velocity effects in atomic and molecular collisions: Study by coherent transients

The effect of translational velocity of active atoms and molecules on the properties of photon echo is investigated using the technique of coherent transient processes. A variation in the photon-echo decay with a frequency detuning of the excitation radiation relative to the center of the vibrational-rotational transition 0 ? 1 ν₃ R(4, 3) is observed in a mixture of ¹³CH₃F with atomic buffers. The results are interpreted using the dependence of the echo decay rate on the magnitude of the translational velocity of active particles. The dependence of the relaxation matrix on the direction of the velocity of active atoms results in a new phenomenon of the collision-induced echo, which is investigated at the transition 0 ? 1 ¹⁷⁴Yb in mixtures with atomic buffers.     

Comparisons of some molecular properties calculated with basis sets of Slater-type orbitals and floating spherical gaussian orbitals for BH3, BH4 -, B2H6, B4H4, C2H2, C2H4, C2H6, CH4, and C3H4

Some one-electron molecular properties are calculated for BH₃, BH₄ ^-, B₂H₆, B₄H₄, CH₄, C₂H₂, C₂H₄, C₂H₆, and C₃H₄. The wave functions used are constructed from minimal basis sets of STO's and FSGO's. The results obtained from the latter wave functions show that the good agreement with the STO values of the molecular energy is not always maintained with one-electron properties.     

Vibrational relaxation time measurements in CH4 and CH4-rare gas mixtures

With a spectrophone vibrational relaxation times in CH₄ and in mixtures of CH₄ with rare gases were measured. Both the amplitude and the phase method were used. The two infrared active modes of CH₄ (ν₄ and ν₃) were investigated separately. The relaxation times, at one atmosphere, after exciting the lowest mode ν₄, were found to be: τ(CH₄-CH₄) = 1.65 μs; τ(CH₄-He) = 1.97 μs; τ(CH₄-Ne) = 8.6 μs; τ(CH₄-Ar) = 12 μs and τ(CH₄-Kr) ≈ 60 μs. From these values one may in that vibrational-rotational (V-R) energy transfer is the dominant relaxation mechanics. By exciting the higher mode the first step in the deactivation of ν₃ was found to be a V-V transfer to the lowest modes ν₄, ν₂.