Ab initio dipole moment and theoretical rovibrational intensities in the electronic ground state of PH3

We report a six-dimensional CCSD(T)/aug-cc-pVTZ dipole moment surface for the electronic ground state of PH₃ computed ab initio on a large grid of 10 080 molecular geometries. Parameterized, analytical functions are fitted through the ab initio data, and the resulting dipole moment functions are used, together with a potential energy function determined by refining an existing ab initio surface in fittings to experimental wavenumber data, for simulating absorption spectra of the first three polyads of PH₃, i.e., (ν₂, ν₄), (ν₁, ν₃, 2ν₂, 2ν₄, ν₂ + ν₄), and (ν₁ + ν₂, ν₃ + ν₂, ν₁ + ν₄, ν₃ + ν₄, 2ν₂ + ν₄, ν₂ + 2ν₄, 3ν₂, 3ν₄). The resulting theoretical transition moments show excellent agreement with experiment. A line-by-line comparison of the simulated intensities of the ν₂/ν₄ band system with 955 experimental intensity values reported by Brown et al. [L.R. Brown, R.L. Sams, I. Kleiner, C. Cottaz, L. Sagui, J. Mol. Spectrosc. 215 (2002) 178-203] gives an average absolute percentage deviation of 8.7% (and a root-mean-square deviation of 0.94 cm⁻¹ for the transition wavenumbers). This is very remarkable since the calculations rely entirely on ab initio dipole moment surfaces and do not involve any adjustment of these surfaces to reproduce the experimental intensities. Finally, we predict the line strengths for transitions between so-called cluster levels (near-degenerate levels formed at high rotational excitation) for J up to 60.     

Determination of vibrational energy levels and transition dipole moments of CO2 molecules by density functional theory

An efficient method is presented to calculate the intra-molecular potential energies and electrical dipole moments of CO₂ molecules at the electronic ground state by solving the Kohn-Sham (KS) equation for a total of 101 992 nuclear configurations. The projector-augmented wave (PAW) exchange-correlation potential functionals and plane wave (PW) basis functions were used in solving the KS equation. The calculated intra-molecular potential function was then included in the pure vibrational Schrödinger equation to determine the vibrational energy eigen values and eigen functions. The vibrational wave functions combined with the calculated dipole moment function were used to determine the transition dipole moments. The calculated results were compared with the experimental data.     

High resolution infrared spectra of the first and second stretching overtone band systems of SbD3

The high resolution infrared spectrum of the mono-isotopic species ¹²³SbD₃ has been studied in the regions of the first and second Sb–D stretching overtones, from 2600 to 2800 cm⁻¹ and from 3900 to 4100 cm⁻¹, respectively. In both regions only two almost degenerate bands of similar intensity have been observed, one parallel and the other perpendicular, corresponding to the low-lying states in the manifolds of the excited vibrational states. These bands have been identified as 2ν₁(A₁)/ν₁ + ν₃(E) in the first overtone and 3ν₁(A₁)/2ν₁ + ν₃(E) in the second overtone band system. About 1700 transitions with have been assigned to the 2ν₁(A₁)/ν₁ + ν₃(E) and about 700 with to the 3ν₁(A₁)/2ν1 + ν₃(E) dyad. The transitions assigned to each dyad have been fitted simultaneously since the A₁/E excited states are affected by strong Coriolis and k-type perturbations treated explicitly in the model. Eventually, the extent to which the parameters resulting from the analyses fulfill the local mode theory requirements has been evaluated. Differently from SbH₃, the deuterated species does not reach true local mode behavior, even in the second overtone.     

Ab initio calculation of accurate dissociation energy, potential energy curve and dipole moment function for the A1∑ + state 7LiH molecule

The reasonable dissociation limit of the A¹∑⁺ state $^{7}$LiH molecule is obtained. The accurate dissociation energy and the equilibrium geometry of this state are calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space for the first time. The whole potential energy curve and the dipole moment function for theA¹∑⁺ state are calculated over a wide internuclear separation range from about 0.1 to 1.4\,nm. The calculated equilibrium geometry and dissociation energy of this potential energy curve are of R_{\e}=0.2487\,nm and D_{\e}=1.064\,eV, respectively. The unusual negative values of the anharmonicity constant and the vibration-rotational coupling constant are of \textit{\omega }_{\e}\textit{\chi }_{\e}=--4.7158cm^{ - 1} and \textit{\alpha }_{\e}=--0.08649cm^{ -1}, respectively. The vertical excitation energy from the ground to the A¹∑⁺ state is calculated and the value is of 3.613\,eV at 0.15875nm (the equilibrium position of the ground state). The highly anomalous shape of this potential energy curve, which is exceptionally flat over a wide radial range around the equilibrium position, is discussed in detail. The harmonic frequency value of 502.47cm¹ about this state is approximately estimated. Careful comparison of the theoretical determinations with those obtained by previous theories about the A¹∑⁺ state dissociation energy clearly shows that the present calculations are much closer to the experiments than previous theories, thus represents an improvement.     

~(39)K_2分子C~1Ⅱ_u-X~1∑_9~+(J′=105)Q支激光诱导荧光光谱及电偶极跃迁矩变化率研究

用4415.6(?)CW激光线获得了~(39)K_2分子C~1II_u(v′=0,J′=105)-X~1∑_g~+(v″=1～10,J″=105)Q支激光诱导荧光(LIF)光谱.用最小二乘法拟合出了~(39)K_2分子X~1∑_g~+态振动常数和C~1II_u态电子谱项值T_e.光谱分析表明C~1II_u态T_e=22968cm~(-1)是合适的.用~(39)K_2分子Morse势计算了(V′=0,J′=105)-(v″=1～10,J″=105)跃迁的Franck-Condon因子和跃迁强度,强度计算值和激光诱导荧光光谱测量值之间有令人满意的符合,进一步的r重心近似分析给出了~(39)K_2分子C~1II_u→X~1∑_g~+电偶极跃迁矩R_(?)随核间距r的归一化变化率为-0.157～-0.168 debye/(?)(4.22(?)相似文献   

Collision-induced absorption in the V2 fundamental band of ^12CH4

The integrated intensities of the collision-induced absorption of the V2 band of ^12CH4 perturbed by Ar have been calculated theoretically using the ab initio calculations, and the value of the quadrupole transition moment we obtained is （0/Q/V2） = 5.226ea^2.. The corresponding experimental value obtained from ^12 CH4-Ar spectra is /〈0/Q/V2）/ = 4.931ea^2. Ignoring vibration-rotation interaction and Coriolis interaction, and considering both the theoretical approximations and experimental uncertainties, the agreement can be regarded as good, thus confirming that the enhancement is due to the quadrupole collision-induced mechanism.[第一段]     

应变对单层二硫化钼能带影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波赝势方法,研究了双轴拉应变下单层二硫化钼晶体的电子结构性质．本文的计算结果表明对单层二硫化钼晶体施加一个很小的应变（0．5％）时,其能带结构由直接带隙转变为间接带隙．随着应变的增加,能带仍然保持间接带隙的特征,且禁带宽度呈现线性下降的趋势．通过对单层二硫化钼晶体态密度和投影电荷密度的进一步分析,揭示了单层二硫化钼晶体能带变化的原因．     

A microwave and ab initio investigation of N2-SO3, OC-SO3, and OC-SO3-Ar

Microwave spectra have been observed for N₂-SO₃, OC-SO₃, Ar-SO₃-CO, and several of their isotopic derivatives. All three complexes are symmetric tops with little or no out-of-plane distortion of the SO₃. In Ar-SO₃-CO, the Ar and CO lie on opposite sides of the sulfur, an arrangement which has not been previously observed for trimers involving SO₃. In N₂-SO₃ and OC-SO₃, the N-S and C-S bond lengths are 2.934(12) and 2.854(12), respectively. In Ar-SO₃-CO, the C-S distance is 2.849(4) Å, which is identical, within the estimated uncertainties, to that in OC-SO₃. The Ar-S distance, on the other hand, is 3.411(11) Å, which represents a small but distinct lengthening of 0.061(12) Å relative to that previously determined for Ar-SO₃. Stark effect measurements for OC-SO₃ and Ar-SO₃-CO give dipole moments of 0.8488(13) and 0.602(15) D, respectively. The latter is very nearly equal to the difference between the dipole moments of OC-SO₃ and Ar-SO₃, suggesting that the dipole moment of the trimer is simply the vector sum of the unperturbed dimer dipole moments. Counterpoise corrected optimized geometries and binding energies have been computed at the MP2/aug-cc-pVTZ level for Ar-SO₃ (1.08 kcal/mol), N₂-SO₃ (2.60 kcal/mol), OC-SO₃ (3.92 kcal/mol), and Ar-SO₃-CO (4.90 kcal/mol). The binding energy of Ar-SO₃-CO is nearly equal to the sum of the Ar-SO₃ and OC-SO₃ binding energies, indicating that the two-body interactions on opposite sides of the SO₃ plane are not strongly coupled. Taken together, the experimental and theoretical results indicate that Ar-SO₃-CO is best regarded as a composite of Ar-SO₃ and OC-SO₃ moieties.     

Calculations of the vibrational frequency and isotopic shift of UF6 and U2F6

Molecular structure, vibrational frequency and infrared intensity of UF6 are investigated by using the revised Perdew Burke-Enzerhof function with the triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of a stable U2F6 molecule with a multiple bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.     

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.     

H2SiCl2 中 SiH 伸缩振动的泛频光谱

在2000 ～ 9000 波数 、 12000 ～12900 波数的光谱区间记录了室温下H2SiCl2气体分子的振动泛频光谱，所用的仪器分别是高分辨傅立叶变换光谱仪和高灵敏激光腔内吸收光谱仪。用局域模模型和包含达林－丹尼生共振的简正模模型，归属了SiH伸缩振动的基频和泛频，振动量子数的改变△VSiH=1, 2, 3, 4 and 6。通过对实验能级的非线性拟合，得到SiH伸缩振动的谐振频率ωm、非谐性常数χm、键间耦合系数λ、莫尔斯振子参数 De、α 和相互作用力常数 。实验发现，随着振动能量的增加，振动簇（manifold，两个SiH键的伸缩振动量子数m+n=常数 ）中能量最低的两个能级的间距逐渐减小。当△VSiH≥4时，在实验误差范围内这两个最低的振动态能级简并。这种简并的能级结构类似双原子莫尔斯振子，符合Birge-Sponer 关系。双原子莫尔斯振子直接描述了H2SiCl2分子中SiH 的高泛频伸缩振动，表明在高振动情况下振动能量已经集中到单个SiH键上。     

Determination of the molecular dipole moment of bromofluoromethane: Microwave Stark spectra and ab initio calculations

The electric dipole moment of bromofluoromethane, CH₂⁷⁹BrF, has been determined with a good accuracy by observing the second order ΔM_J = 0 Stark spectrum of the J = 3_2,1 ← 3_1,2, J = 5_2,3 ← 5_1,4 and J = 5_2,4 ← 5_1,5 rotational transitions. In addition, the equilibrium geometry and dipole moment have been evaluated using highly accurate ab initio calculations. By comparing the experimental [μ_a = 0.3466(11) D and μ_b = 1.704(26) D] and theoretical [μ_a = −0.339 D and μ_b = −1.701 D] dipole moment components, a very good agreement has been found.     

Measurements of line intensities and determination of transition moment parameters from experimental data for the ν1 and ν3 bands of D2S

First measurements of line intensities for ν₁ and ν₃ bands of D₂³²S are reported. About 300 intensities of D₂³²S vibration–rotation lines were obtained from experimental high-resolution spectra recorded in the 1810–2051 cm⁻¹ region with the Fourier Transform Spectrometer built in Reims. Empirical values of transition moment parameters for ν₁ and ν₃ bands of D₂³²S were determined for the first time using a least-square fit to the observed intensities. Experimental D₂³²S intensities were compared with recent global variational predictions [Vl.G. Tyuterev, L. Régalia-Jarlot, D.W. Schwenke, S.A. Tashkun, Y.G. Borkov, C. R. Phys. 5 (2004) 189–199] computed from isotopically invariant potential and dipole moment functions of the hydrogen sulphide molecule. Average discrepancy between these calculations and our observed data was 0.03 cm⁻¹ for line positions of this spectral range. The discrepancy between these calculations and our measurements for the sum of line intensities was 5.5% and 3.5% for the ν₁ and ν₃ bands, correspondingly.     

CNDO/2 and INDO all-valence-electron calculations on the dipole moment of iodine compounds

An application of the semi-empirical CNDO/2 and INDO methods to calculate the molecular dipole moment of iodine compounds has been made with all-valence electron scheme. Equilibrium geometries are obtained using experimental bond lengths and the various semi-empirical parameters required inscf-mo scheme are obtained from atomic Hartree-Fock calculations and by comparison withab initio calculations. Bothsp andspd valence basis sets are used.     

Line frequencies and intensities in the ν3 fundamental band of molecules with an octahedral symmetry

Frequencies and lines intensities in the υ₃ band of molecules with an octahedral symmetry have been calculated by the use of second-order perturbation theory, according to the model of clusters. The calculations are developed by the use of the Hamiltonian of Hecht and the special properties of these molecules. Comparisons are made between the present theoretical calculations and other theoretical and experimental works.     

Determination of electric dipole moment for the ν2 vibrational state of 15NH3 by infrared-infrared double resonances

An infrared-infrared double-resonance technique, employing the sidebands produced by electro-optic amplitude modulation of a single-frequency CO₂ laser, is used to observe the second-order Stark effect of the ν₂asR(2, 0) transition of ¹⁵NH₃. The technique enables the Stark shifts in ground and vibrationally excited states to be observed separately and yields the electric dipole moments: μ(v₂ = 1) = 1.253 ± 0.003 D, μ(v = 0) = 1.469 ± 0.004 D. The relative intensity distribution, linewidths, and line shapes of features in the double-resonance Stark spectra are also examined.     

Transition dipole moment measurements for the ν2 band of NH3 with molecular beam laser Stark spectroscopy

Rabi oscillations were observed in the ASR(110), ΔM = 0 and ASQ(222), ΔM = 0 transitions of the ν₂ band of ¹⁴NH₃ in a molecular beam crossed by a CO₂ laser beam. The frequency (in terms of the laser field amplitude) of the oscillations was used to determine the transition dipole moment of the ν₂ band, yielding μ_s←a = 0.261 ± 0.006 D. The hyperfine structure due to the electric quadrupole interaction of the nitrogen nucleus was clearly resolved.     

Spectral intensities in the ν1 band of NH3

Intensities have been measured for individual transitions in the Q and R branches of the ν₁ band of NH₃ using a difference-frequency laser spectrometer. The data yield an integrated band strength of S⁰_v=219.36±1.03 cm^-2/MPa at 297 K, corresponding to a transition moment of μ_v = 8.535(20) × 10^-32 C·m, and a Herman-Wallis correction factor, (1 + _jm)², where _j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν₄ (E, L = 2), so were excluded from the fit. A small sample of ν₃ band lines occurring in the ν₁ band scans also yields a rough estimate of the ν₃ band intensity with evident irregular perturbations.     

Analysis of the CIA spectra of the first overtone band of D2 in D2-N2

Enhancement spectra of the collision-induced absorption (CIA) in the first overtone region 5000-7000 cm⁻¹ of D₂ in D₂-N₂ were studied at 298 K for a base density of D₂ of 73 amagat and for partial densities of N₂ in the range 150-370 amagat. The observed spectra were modeled with a total of 1176 components of double vibrational transitions. Binary and ternary absorption coefficients were determined from the integrated absorption of the band. Profile analysis of the spectra was carried out using the Birnbaum-Cohen line-shape function for the individual components of the band, and characteristic line-shape parameters were determined from the analysis. Good agreement was obtained between the experimental and calculated spectral profiles.