A NONLINEAR MODEL FOR HIGHLY EXCITED VIBRATIONAL ENERGY LEVELS OF SILANE

The highly excited vibrational energy levels of SiH stretches of silane SiH₄ in the electronic ground state are calculated using a three-parameter nonlinear model, i.e., the quantized discrete self-trapping equation. The obtained results are in good agreements with the experimental data and with those obtained from local mode calculations of others. We note that SiH₄ molecule is a typical molecule close to the local mode limit, and that when n≥3, the molecule could be thought of as vibrating with the four SiH stretching quanta trapped into a single SiH bond.     

Study on high-temperature spectra of asymptotic asymmetric-top radical SiO2

Total internal partition sums are calculated in the product approximation at temperatures up to 6000 K for the asymptotic asymmetric-top SiO2 molecule.The rotational partition function and the vibrational partition function are calculated with the rigid-top model and in the harmonic oscillator approximation,respectively.Our values of the total internal partition sums are consistent with the calculated value in the Gaussian program within 0.137% at 296 K.Using the calculated partition functions and the rotationless transition dipole moment squared as a constant,we calculate the line intensities of 001-000 band of SiO2 at normal,medium and high temperatures.Simulated spectra of the 001-000 band of the asymptotic asymmetric-top SiO2 molecule at 2000,5000 and 6000 K are also obtained.     

超快二维红外光谱用于研究单体水分子中的直接振动能量传递

Vibrational relaxation dynamics of monomeric water molecule dissolved in d-chloroform solution were revisited using the two dimensional Infrared (2D IR) spectroscopy. The vibrational lifetime of OH bending in monomeric water shows a bi-exponential decay. The fast component (T₁=(1.2±0.1) ps) is caused by the rapid population equilibration between the vibrational modes of the monomeric water molecule. The slow component (T₂=(26.4±0.2) ps) is mainly caused by the vibrational population decay of OH bending mode. The reorientation of the OH bending in monomeric water is determined with a time constant of τ=(1.2±0.1) ps which is much faster than the rotational dynamics of water molecules in the bulk solution. Furthermore, we are able to reveal the direct vibrational energy transfer from OH stretching to OH bending in monomeric water dissolved in d-chloroform for the first time. The vibrational coupling and relative orientation of transition dipole moment between OH bending and stretching that effect their intra-molecular vibrational energy transfer rates are discussed in detail.     

CALCULATIONS OF STRETCHING VIBRATIONAL ENERGY LEVELS OF THE CH3I MOLECULE BY A NONLINEAR MODEL

A nonlinear model, i.e. the quantized discrete self-trapping equation, is applied to calculate the highly excited CH stretching vibrational energy levels of the CH₃I molecule in the liquid phase at the electronic ground state up to n=8. The obtained results agree well with the experimental data and with those obtained from local mode model calculations. We note that the dominant feature of the methyl CH stretching vibrational energy levels of the CH₃I molecule is a pattern of local mode pairs. When n≥7, all the vibrational energy of the CH₃ group can nearly be localized on a single CH bond.     

Spectroscopic Detection of Sulfur Oxides in the Aircraft Wake

The absorption/emission spectral regions of SO, SO₂, SO₃, S₂O and HSO are analyzed for the range from UV (λ ≥ 0.2 μm) to IR (λ < 30 μm) and are compared with the atmospheric transmission spectrum. It is shown that many vibrational bands of the compounds considered fall into atmospheric transmission windows. For the vibrational bands of SO, SO₂, SO₃, S₂O, and HSO molecules there are some gases which hinder the absorption diagnostics of the indicated compounds. These interfering gases are natural components of atmospheric air as well as specific gases of aircraft engine exhaust. It is found that the least influence of the interference takes place in the 2400–2700 cm⁻¹ IR region. The spectroscopic techniques used for the detection of aircraft engine exhaust compounds are briefly reviewed, with much consideration given to SO₂. The IR absorption spectra of SO₂ and other gases are calculated for the conditions of the aircraft engine nozzle exit. Narrow spectral intervals suitable for SO₂ detection in a hot flow are determined. An analysis is made for the detection capabilities of CO₂ lasers (including isotope CO₂ lasers) and CO lasers (both fundamental band and first-overtone ones) as applied to SO₂ detection in aircraft engine exhaust. Published in English as Preprint No. 5 of the P. N. Lebedev Physical Institute, Moscow (2004).     

CALCULATIONS OF STRETCHING VIBRATIONAL OVERTONES AND COMBINATIONS OF ARSINE BY NONLINEAR MODEL

A three-parameter nonlinear model in nonlinear quantum theory,i.e.,the quantized discrete self trapping equation, has been used to calculate the vibrational energy spectrum, including the overtones and combinations with many excited quanta, of AsH stretches of arsine, AsH₃. The model calculations agree well with experiment and other calculations. It is shown that the dominant feature of the energy spectrum of AsH₃ molecule is a pattern of local mode pairs, and that when n≥4, all the vibrational energies are almost localized on a single AsH bond.     

一氧化二氮分子位于775 nm的6υ3振动泛频跃迁的高精密光腔衰荡光谱

Transitions of the 6υ₃ overtone band of ¹⁴N₂ ¹⁶O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10^-4 cm^-1 allowed us to reveal finer ro-vibrational couplings taking place after J>14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6υ₃ band obtained in this work and those from previous studies is given.     

Study on High-Temperature Spectra of Asymptotic Asymmetric-Top Molecule O3

The line intensities of 001-000 transition of the asymptotic asymmetric-top Oa molecule at several temperatures are calculated by directly calculating the partition functions and regarding the rotationless transition dipole moment squared as a constant. The calculated values of the total internM partition sums （TIPS） are consistent with the data of HITRAN database with -0.61% at 296 K. The calculated line intensity data at 500 K and 3000 K are also in excellent agreement with the data in HITRAN database with less than 0.659% and 5.458% at 500 K and 3000 K, which provide a strong support for the calculations of partition function and fine intensity at high temperature. Then we extend the calculation to higher temperatures. The line intensities and simulated spectra of v3 band of the asymptotic asymmetric-top O3 molecule at 4000 and 5000 K are reported. The results are of significance for the studying of the molecular high-temperature spectrum including experimental measurements and theoretical calculations.     

Vibrational Spectroscopy of CH/CD Stretches in Propadiene: An Algebraic Approach

Using Hamiltonian based on Lie algebraic method, the stretching vibrational modes of C3H4 and C3D4 molecules are calculated up to higher overtones. The model appears to describe C-H and C-D stretching modes with less number of parameters. The locality parameter ξ confirms the highly local behaviour of the stretching modes of these molecules.     

Algebraic Hamiltonian for Vibrational Spectra of Stibine

An algebraic Hamiltonian, which in a limit can be reduced to an extended local mode model by Law and Duncan, is proposed to describe both stretching and bending vibrational energy levels of polyatomic molecules, where Fermi resonances between the stretches and the bends are considered. The Hamiltonian is used to study the vibrational spectra of stibine (SbH3). A comparison with the extended local mode model is made. Results of fitting the experimental data show that the algebraic Hamiltonian reproduces the observed values better than the extended local mode model.     

Calculation of dipole moment functions with density functional theory: application to vibrational band intensities

We have calculated fundamental and overtone XH stretching vibrational band intensities for H₂O, benzene, cyclohexane, 1,3-butadiene, and HCN. The band intensities were calculated with a simple harmonically coupled anharmonic oscillator local mode model and a series expanded dipole moment function. The dipole moment functions were obtained from local, non-local and hybrid density functional theory calculations with basis sets ranging from 6–31G(d) to 6–311++G(3df,3pd). The calculated band intensities have been compared with intensities calculated with conventional ab initio methods and with experimental results. Compared with conventional correlated ab initio methods, a carefully chosen density functional method and basis set seems to give better fundamental and overtone intensities with far less resources used. We have found that the density functional methods appear to be less sensitive to the choice of basis set, with little difference between the results obtained with a non-local or hybrid density functional method.     

Transition moments and NH2 cometary spectra

We calculate vibronic transition moments for the A^?2A_1-X^?2, electronic band system, and for the vibrational transitions within the à and [Xtilde] states, of the NH₂ free radical with the purpose of assisting in the quantitative interpretation of cometary NH₂ emission spectra. To do this it is necessary to use molecular wavefunctions, and electric dipole moment and transition moment surfaces. The wavefunctions are obtained using our program system RENNER after we have determined optimized à and [Xtilde] state potential energy surfaces in a fitting to data. We have obtained the electric dipole moment and transition moment surfaces by ab initio calculation.     

Spectroscopy and dynamics of the isolated sp2 CH chromophore in trideuteroacetaldehyde CD3CHO as derived from extrapolated SDCI ab initio calculations

Ab initio CI potential energy (PES) and dipole moment (DMS) surfaces have been calculated with singles and doubles excitation configuration interaction (SDCI) for the 2-dimensional isolated sp² CH chromophore subspace of trideuteroacetaldehyde (CD₃CHO). Different extrapolation schemes to full-CI have been applied after the extrapolation to full-SDCI. Vibrational band centres and absolute intensities are determined variationally on six extrapolated surfaces. The band centres are analysed within the effective Hamiltonian model for isolated CH chromophores and the effective spectroscopic parameters are compared for the different extrapolation schemes. Time dependent population evolution for vibrational quantum motion with a pure CH stretching state being initially populated is calculated for some of the extrapolated surfaces within the effective Hamiltonian model.     

Variation of Dipole Moment Function of O-H Bond of t-Butanol with the Nature of Solvent and Its Temperature

The intermolecular influence on dipole moment function is evaluated for O-H bond of t-butanol in different nonpolar solvents at temperatures ranging from 10° to 60°C employing IR band intensities of fundamental and first overtone bands. Two sets of dipole moment derivatives have been calculated corresponding to – and +- combinations of the transition moment matrix elements R₁₀ and R₂₀, the values for ++ and -+ combinations are equal in magnitude to those for - and +- combinations, respectively and opposite in signs. In general the dipole moment derivatives increase on lowering the temperature as well as with increasing molecular interactions with the solvent molecules. Dipole moment plots with dimensionless coordinate ξ [=(r-r_e)/r_e, where r and r_e are internuclear distances during vibration and at equilibrium, respectively] are reported for various systems considered. It is found that for +- combination the dipole moment maximum shifts to higher internuclear distances when polarisation of the solute molecules is increased by lowering of temperature or increase in molecular interactions between solute and solvent molecules. A reverse trend is observed for – combination.- The OH band of t-butanol vapor has been measured.     

Determination of the dipole moment function of an ozone molecule on the basis of vibrational transition probabilities

Analytical relationships are obtained that connect the vibrational transition moments to molecular and electrooptical parameters. On the basis of experimental data on vibrational band intensities, coefficients of the expansions of the dipole moment function of O₃ are determined by using the above-mentioned expressions.     

对称陀螺分子NH3的高温谱线强度研究

在直接计算分子配分函数的基础上，将无转动跃迁偶极矩平方近似为一常数，计算了对称陀螺分子NH₃ 0300 a—0000 s跃迁在高温下的线强度.在296K，计算的分子总配分函数与HITRAN数据库的结果符合很好，只有0.19%的百分误差.计算的跃迁线强度在2000 K和3000K的高温与HITRAN数据库的结果也符合相当好，最大百分误差分别为-0.65%和-1.77%.这就表明分子配分函数和线强度的高温计算是可靠的.在此基础上，计算被扩展到更高温度，报道了对称陀螺分子NH_{3< 关键词： 高温光谱 对称陀螺分子 配分函数 氨}     

Rotational energy cluster formation in XY3 molecules: Excited vibrational states of BiH3 and SbH3

Previous theoretical work on energy cluster formation at high rotational excitation in the vibrational ground state of PH₃ [S.N. Yurchenko, W. Thiel, S. Patchkovskii, P. Jensen, Phys. Chem. Chem. Phys. 7 (2005) 573] is extended to BiH₃ and SbH₃. By means of variational calculations of the rotation–vibration energies based on ab initio potential energy surfaces, we analyze the rotational energy clustering of BiH₃ and SbH₃ at J  70 for a number of vibrational states. We show that BiH₃ and SbH₃, with their pronounced local mode behaviour, exhibit cluster formation already at moderate rotational excitation. In addition, owing to its quasi-spherical-top character, BiH₃ undergoes an imperfect bifurcation at high J. This gives rise to an energy cluster type not present in PH₃ and SbH₃. We present a semi-classical approach to the construction of the rotational energy surfaces for vibrationally excited states.     

Theoretical study of structural and energy parameters of the van der Waals complex of the Li<Superscript>+</Superscript> cation with the N<Subscript>2</Subscript> molecule

The three-dimensional vibrational problem for the isolated van der Waals complex formed by the Li⁺ cation with the N₂ molecule is solved by the variational method. The potential energy and dipole moment surfaces are calculated using different basis sets of atomic functions and different approaches for taking electron correlation into account. The anharmonic effects caused by the interaction of vibrational degrees of freedom of the complex are consistently considered for the first time. The energy levels of three-dimensional vibrational states are determined. The frequency shift of the N₂ molecule vibration upon complexation and the fundamental transition intensity for this vibration in the complex are calculated. The frequencies and intensities for a number of spectral transitions between the states associated with excitation of low-frequency modes are determined. The average values of geometrical parameters and their variances are calculated for the ground state and excited vibrational states of the complex.     

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.