Theoretical calculation of the dipole moment function of the a4Π state of NO

The potential energy curve and theoretical dipole moment function of the a⁴Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a⁴Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N⁺O^?. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr.     

Moments de transition vibrationnelle des molecules diatomiques. Intensite des raies rovibrationnelles des bandes 0→2 et 0→3 et fonction dipolaire de CO

General expressions for the radial wavefunctions and the rotationless matrix elements of the dipole moment for the transitions 0→0 to 0→4 are obtained using a fifth-power internuclear potential, a quartic dipole moment function, and third-order perturbation theory. Line intensities in the 0→2 and 0→3 bands of CO have been measured for pressures varying from 2 to 5 atm. Using the values of the vibrational transition moments |R₀²| and |R₀³| deduced from our measurements and the values of |R₀⁰|, |R₀¹| and |R₀⁴| previously given, we evaluate the coefficients M₀ to M₄ of the dipole-moment function for CO.     

On the theory of the ionization-induced drag of fast charged particles

The moments in the theory of deceleration of fast charged particles colliding with an oscillator have been considered in the dipole approximation. In this approximation, the problem has been solved exactly, and the moment of the oscillator has been determined from the initial state |m> = |0> in the form of the sum of 1D integrals. The method considered here makes it possible to calculate the moments for ion velocities close to atomic velocities (v ~ v_a).     

Radial matrix elements and dipole moment function for the ground state of CO

Radial matrix elements 〈vJ|x^k|v′J′〉 for k = 0–5, v = 0–12, |v′- v| = 0–4, and J up to 150 have been calculated for CO using accurate wavefunctions obtained from the numerical solution of the Schrödinger equation with a second-order RKR potential curve. These are used in conjunction with a model dipole moment function (a Padé approximant which has the correct united and separated atom limits and R^?4 long-range behavior) to analyze the experimental intensity data. For all the levels considered, we conclude that an adequate representation of the dipole moment function is provided by a five-term power series expansion. This simplifies the computation of dipole moment matrix elements, typical results of which are presented to illustrate the dependence on the rotational and vibrational quantum numbers.     

Microwave spectrum, structure, and dipole moment of the trans-trans isomer of methylpropylether

Microwave spectra of the trans-trans (TT) isomer of methylpropylether and its 12 isotopically substituted species were measured. The r_s structure of this isomer was determined from the observed moments of inertia. Structural parameters of this isomer were roughly equal to those of the reported r_s structures of trans-ethylmethylether and propane. Dipole moments of the TT isomer for the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment was μ_a = 0.082 ± 0.010, μ_b = 1.104 ± 0.013, and μ_total = 1.107 ± 0.013 D making angles of 4°17′ with the b-inertial axis, of 6°7′ with the bisector of the COC angle. The barrier to internal rotation of the CH₃C group was calculated to be 3300 ± 60 cal/mole from A-A splittings of the spectra in the CH₃C excited torsional state.     

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.     

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.     

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.     

Microwave spectrum and conformation of 6-thiabicyclo[3.1.0]hexane

The microwave spectrum of 6-thiabicyclo[3.1.0]hexane (cyclopentene sulfide) has been measured in the region 26,500-40,000 MHz. The experimental data are consistent with a single stable conformation. Furthermore, these data can only be satisfactorily explained by assuming that this conformation is the boat form. Rotational constants were obtained, both for the ground state and two excited vibrational states, while centrifugal distortion coefficients were obtained for the ground state and one excited vibrational state. The ground state rotational constants found were A₀ = 5026.243 ± 0.003 MHz, B₀ = 2833.813 ± 0.003 MHz, and C₀ = 2411.679 ± 0.03 MHz. For the ground state of the molecule, the electric dipole moment components were found to be μ_a = 1.800 ± 0.012 D and μ_c = 1.155 ± 0.024 D, yielding a total dipole moment μ = 2.139 ± 0.027 D.     

Theoretical study of the electronic states and transition dipole moments of the LiK molecule

The adiabatic potential energy, the spectroscopic constants and the transition dipole moments of the lowest electronic states of the LiK⁺ molecule, dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s, and 4p) + K⁺ and Li⁺ + K(4s, 4p, 5s, 3d, 5p, 4d, and 6s), have been investigated. We have used an ab initio approach involving a non-empirical pseudopotential for the Li (1s²) and K (1s²2s²2p⁶3s²3p⁶) cores and core valence correlation correction. A very good agreement has been obtained for the ground state for the spectroscopic constants with the available theoretical works. The transition dipole moment from X²Σ, 2²Σ, 3²Σ, and 4²Σ states to higher excited states have been determined. Numerous avoided crossing between electronic states of ²Σ and ²Π symmetries, have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Li⁺K and LiK⁺.     

Theoretical integrated intensities for the 2ν2 and 2ν2-ν2 bands of HCN and DCN

Dipole moment functions, both perpendicular and parallel to the molecular axis, are calculated from the SCF and MRD-CI results of a previous study for the normal ν₂ bending vibrations of HCN and DCN. Vibrationally averaged dipole moments and the infrared transition matrix elements are then obtained from the dipole moment functions and vibrational wave functions. MRD-CI results, with known experimental values in parentheses, for HCN are 〈0|μ|0〉 = ?2.954(?2.985) D, 〈1|μ|1〉 = ?2.915(±2.942) D, 〈0|μ|1〉 = 0.148(0.147) D, 〈0|μ|2〉 = ?0.027 D, 〈1|μ|2〉 = 0.210 D. Calculated absolute intensities at 1 atm and 0°C for the (02⁰0) ← (000), (02⁰0) ← (010), and (02²0) ← (010) bands of HCN are 25 (40 ± 10 as estimated from spectra), 8.5, and 17.0 atm^?1 cm^?2, respectively. Results for DCN are also reported.     

Barriers to internal rotation in asymmetric molecules: 2,3-Difluoropropene

The potential function for internal rotation in 2,3-difluoropropene has been obtained from the microwave spectrum of the gauche rotamer, the far- and mid-infrared spectra of both the gauche and cis rotamers and the absolute rotational intensity measurements of several gauche microwave transitions. It is found that the cis conformer is most stable by 145 ± 60 cm⁻¹. Both the cis-gauche and gauche(+)-trans-gauche(−) barriers are approximately 1000 cm⁻¹. A comparison between the potentials in 2,3-difluoropropene, propene, and several other fluoropropenes is made. The dipole moment of the gauche conformer is μ_a = 0.950 D, μ_b = 1.982 D, and μ_c = 1.135 D; μ_total = 2.67 D.     

The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

Microwave spectrum,dipole moment,and structure of 3-aminopropanol

The microwave spectra of 3-aminopropanol and three of its deuterium substituted isotopic species have been investigated in the 26.5 to 40 GHz frequency region. The rotational spectrum of only one conformer has been assigned in which presumably a hydrogen bond of the OH---N type exists. The rotational spectra of a number of excited vibrational states have been observed and assignments made for some of these excited states. The average intensity ratio for the rotational transitions between the ground and excited vibrational states indicates that the first excited state is about 120 cm^?1 above the ground state.and the next higher state is roughly 200 cm^?1 above the ground vibrational state. The dipole moment was determined from the Stark effect measurements to be 3.13 ± 0.04 D with its principal axes components as |μ_a| = 2.88 ± 0.03 D, |μ_b| = 1.23 ± 0.04 D and |μ_c| = 0.06 ± 0.01 D. The possibility of another conformer where the hydrogen bond could be of NH---O type was explored, but the spectra of such a conformer could not be identified.     

The Electric Dipole Moment of the CO2–CO van der Waals Complex

Radiofrequency transitions withinK= 2 asymmetry doublets have been observed for the CO₂–CO van der Waals complex. A Stark effect measurement on theJ= 2,K= 2 transition provides an electric dipole moment of μ = 0.2493(1) D. Combining this result with the permanent moment of CO, μ_CO= 0.1098 D, gives a change of moment on complex formation of Δμ = 0.140 D. The sign of Δμ is such that the CO end of the complex is more positive than CO₂. The origin of Δμ should not be attributed to any single mechanism, and several different contributions to Δμ are discussed.     

The dipole moment of water: Stark effects in D2O and HDO

The dipole moment of D₂O has been determined from Stark effect measurements for the 3₁₃–2₂₀ and 4₄₁–5₃₂ microwave transitions as 1·857 ± 0·006 and 1·869 ± 0·005D respectively. A rotational dependence of dipole moment has also been established for HDO through μ_a in the 2₂₀–2₂₁ and 5₃₂–5₃₃ transitions; μ_a was determined as 0·662 ± 0·001 and 0·644 ± 0·001D respectively. The total dipole moment for HDO has been determined from the 3₂₁–4₁₄ transition to be 1·85 ± 0·01D and to lie within 0·1° of the bisector of the HOD angle. High resolution Stark spectroscopy has been performed on the 6₂₄–6₁₅ transition of D₂O with improved precision using the 337 μm emission line of the HCN laser. This experiment has confirmed the dipole results from the microwave work and the frequency of the 6₂₄–6₁₅ transition in D₂O has been determined as 890 395 ± 3 MHz.

The slight increase of dipole moment with deuteration is consistent with the dipole moment for H₂O determined from the dielectric constant. This increase is discussed for the vibrational ground state (as for ammonia) in terms of anharmonicity in the bending vibration. The change of μ with rotational transition is interpreted in terms of large changes in molecular geometry for certain rotational states due to centrifugal distortion.     

Direct fit of experimental ro-vibrational intensities to the dipole moment function: Application to HCl

A dipole moment function (DMF) for hydrogen chloride (HCl) has been obtained using a direct fit approach that fits the best available and appropriately weighted experimental data for individual ro-vibrational transitions. Combining wavefunctions derived from the Rydberg-Klein-Rees (RKR) numerical method and a semi-empirical DMF, line intensities were calculated numerically for bands with Δv=0, 1, 2, 3, 4, 5, 6, 7 up to v′=7. The results have demonstrated the effectiveness of inclusion of rotational dipole moment matrix elements and appropriate weighting of the experimental data in the DMF fitting. The new method is shown to be superior to the common method of fitting only the rotationless dipole moment elements, while at the same time being simple to implement.     

Methyl and skeletal torsion interaction in methyl thiolfluoroformate

The microwave spectrum of methyl thiolfluoroformate (FCOSCH₃) is reported for the ground state and seven vibrational satellites. The methyl group is in the syn conformation to the carbonyl group. The dipole moment components are μ_a = 2.89(2) D, μ_b = 0.30(8) D, and μ_c = 0. Spacings of A and E levels due to methyl internal rotation are analyzed for the ground state, the first excited methyl torsional state, and the first excited skeletal torsional state. An anomalous sequence of A and E levels occurring in the latter satellite arises from torsional interaction, according to two-dimensional model calculations. Potential parameters consistent with the three observed level separations are V₃ = 304(5) cm⁻¹, V₆ = 23(1) cm⁻¹ for the methyl torsion and either k = 1.912 or k = 2.936 cm⁻¹ deg⁻² for the skeletal torsional force constant.     

Conformation and dipole moment of tetrahydropyran-4-one by microwave spectroscopy

The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ～ 100 cm^?1 above the ground state for the first excited state of the ring-bending and ～ 185 cm^?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μ_a| = 1.693 (0.001), |μ_b| = 0.0, |μ_c| = 0.300 (0.013) yielding a total dipole moment μ_tot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.     

Dipole Moments of 4′-Aminoflavonol Fluorescent Probes in Different Solvents

Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4-(dimethylamino)-3-hydroxyflavone (FME), and 4 N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (_g) and excited Franck-Condon state (_e^FC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0–17.7) × 10^–30 C m. Upon optical excitation, the dipole moments increase by (41.9–52.9) ×10^–30 C m. The value of the change of the dipole moment vector ^a with excitation to the Franck-Condon state and the value of the vector _e^FC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity.