Temporal dependence of the dipole moment of long-wavelength forms of n-dimethylaminobenzonitrile

The temporal dependences μ_e(t) of the dipole moment of n-dimethylaminobenzonitrile excited to different states by quanta with different energies are evaluated based on the experimental correlation functions of the shift of instantaneous spectra. It is found that, upon excitation into the maximum of absorption, the relaxation changes of the spectra are accompanied by an increase in the dipole moment from 9 D in the Franck-Condon state to 16 D in the stationary state. At the same time, the excitation of luminescence at the red absorption edge by radiation at 403 nm leads to a decrease in the range of variation of the dipole moment. In this case, the initial value of the dipole moment amounts to 14 D and, during the lifetime of the excited state, it increases to 17 D. This indicates that the nature of the radiation excited at the wavelength 403 nm is directly related to internal charge transfer states of n-dimethylaminobenzonitrile.     

The dipole moment of the FO radical

The electric dipole moment of the FO radical (${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$) has been directly measured by observing its saturated absorption laser magnetic resonance spectrum (v = 1 ← 0) in the presence of a moderate electric field. The resulting dipole moment [μ(v = 0) = 0.0043(4) D, μ(v = 1) = 0.0267(9) D] is extremely small, and shows a large relative change with vibrational state. The sign of the dipole moment is the same for the two vibrational states. Previous failures to detect microwave or gas phase EPR spectra of FO are fully explained by this small dipole moment.     

Microwave spectrum of (cyanomethyl) cyclopropane

The microwave spectrum of (cyanomethyl) cyclopropane has been studied. Only the gauche form of the molecule has been observed. This is consistent with the infrared results where the gauche form is found to be the dominant form (>85%). The rotational constants for the ground vibrational state are (in MHz) A = 10 800.703, B = 2014.942, C = 1835.685. From Stark effect measurements, the dipole moment is found to be 3.89 ± 0.08 D. Rotational transitions in several excited vibrational states also have been measured and assigned.     

The 5V(OH) Overtone Transition of HDO

The absorption spectrum of HDO has been recorded by intracavity laser absorption spectroscopy in the 16 540-17 055 cm(-1) spectral region corresponding to the 5nu(3) band centered at 16 920 cm(-1). The (0 0 5) vibrational state is found to be mostly isolated from the nearby rovibrational states. The corresponding rovibrational transitions were analyzed and fitted in the frame of the effective rotational Hamiltonian model in Pade-Borel approximants form. The spectroscopic parameters retrieved from the fitting reproduce 100 of the 109 determined energy levels with the root-mean-square deviation of 0.0072 cm(-1), close to the experimental accuracy. From the integrated relative intensities of a- and b-type transitions, the angle between the transition moment and the OH bond is estimated to be 46.4 degrees. This value is consistent with an increasing tilt of the transition dipole moment, away from the OH bond, when the OH stretching is excited. The evolution of the orientation of the transition dipole moment versus the vibrational excitation is then compared for the OH and OD overtone bands. Copyright 2000 Academic Press.     

THz measurements of propane

Propane is present in many planetary atmospheres, as confirmed by vibrational spectroscopy in the infrared wavelengths. As the simplest alkane with a permanent dipole moment, propane has a rotational spectrum. The relatively light atom framework causes the strongest rotational transitions to appear in the submillimeter wavelength range. This fact, as well as the small dipole moment, have prevented the molecule from being observed in the interstellar medium. Telescopes with high sensitivity at high altitude such as the Atacama Large Millimeter Array or above the Earth’s atmosphere like the Herschel Space Observatory are likely to be sensitive enough for detection of this species in the interstellar medium, planetary nebulae, hot cores and/or planetary atmospheres. We present the rotational spectra of propane in its ground and first two excited vibrational states, measured through 1.6 THz. The ground state submillimeter spectrum is approximated well by semi-rigid rotor. The submillimeter data has been combined with high resolution centimeter wavelength data to enable analysis of the equivalent dual-hindered rotor torsional substates using a simplified version of a symmetric two-top Hamiltonian. The same model has been applied to the torsionally excited states that experience more large-amplitude motion and require additional tunnelling parameters.     

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.     

Absorption coefficients for hydrogen—III. calculated pressure-induced H2-H vibrational absorption in the fundamental region

The coefficient for absorption during H₂-H collisions was calculated for temperatures from 2000 to 7000 K and wave numbers between 100 and 40 000 cm^-1 for LTE. Because only transitions with Δν = 1 were considered, the absorption was near the fundamental at 4161 cm^-1 in the infrared. The model included mechanical anharmonicity, vibration-rotation interaction, excited vibrational states, and transverse components of the dipole moment. At 5500 cm^-1, 3750° K, and 1 atm pressure, inclusion of H₂-H vibrational absorption increased the absorption of pure hydrogen gas 48 per cent. An approximate formula for the H²-H absorption coefficient is given for rapid calculation.     

Theoretical study of the spectral and structural parameters of van der Waals complexes of the Li+ cation with the H2, D2, and T2 isotopomers of the hydrogen molecule

The three-dimensional vibrational problem for the isolated binary complexes formed by the Li⁺ cation with all the isotopomers of the hydrogen molecule is solved by the variational method using sufficiently exact nonempirical adiabatic surfaces of the potential energy and the dipole moment. Information on the largeamplitude vibrations was obtained for the first time, and the anharmonic effects caused by the interaction of the different internal degrees of freedom in these weakly bound van der Waals complexes were consistently taken into account. The frequencies and intensities of many spectral transitions are determined, and the average values of geometrical parameters and the dipole moment are calculated for the ground and excited vibrational states.     

Molecular nanocluster fluorescence in microwave infrared-radiation fields

The paper considers a donor-acceptor nanocluster fluorescing in a microwave infrared radiation field. It is assumed that the nanocluster consists of two dipole-dipole interacting organic molecules. It is shown that the fluorescence process of the nanocluster occurs if the donor molecule contains a substructure of identical diatomic pairwise interacting bonds of dipoles (an IR antenna). This antenna is capable of accumulating vibrational energy as a sum of collective vibrational quanta (excimols). The acceptor molecule has no permanent dipole moment and cannot be excited by microwave IR radiation. This molecule is polarized in the dipole moment field of the donor IR antenna and can receive energy accumulated in the IR antenna of the donor molecule. If the acceptor molecule has an electronically excited state in the long-wavelength visible region of its absorption spectrum, then after receiving energy equal to the energy of this state from the donor antenna, the electronic excitation of the acceptor molecule and its fluorescence is possible. As an example, the fluorescence of a nanocluster is considered whose donor molecule has a C _n H_2n IR antenna. The acceptor molecule is aromatic and the external infrared frequency, 1.1 × 10¹⁴ s^?1, is equal to the frequency of the excimol in the donor infrared antenna.     

High-resolution laser Stark and Fourier transform spectroscopy of the ν2 fundamental band of HFCO

The ν₂ (CO stretch) fundamental band of formyl fluoride (HFCO) was studied in the region 1800 to 1910 cm^?1 using the two techniques of intracavity CO laser Stark spectroscopy at sub-Doppler resolution and Fourier transform spectroscopy at Doppler-limited resolution. Accurate values of the molecular parameters of the ground and excited (v₂ = 1) vibrational states were obtained from a combined fit of the ν₂ band data and available microwave data. The results include precise determinations of the electric dipole moment components (μ_a and μ_b) of HFCO in the ground and excited states.     

Spectra and structure of small ring compounds. Microwave spectrum of cyanocyclobutane

The rotational spectrum of cyanocyclobutane has been investigated in the region 18.0–40.0 GHz. Only A-type transitions were observed. R-branch assignments have been made for the ground state and the first three excited states of the ring puckering mode as well as the first two excited states of the out-of-plane cyano-bending mode. The microwave data are consistent with a bent equilibrium ground state for the ring with the cyano-group in the equatorial position. The dipole moment components were determined to be μ_a = 4.04 ± 0.09 D and μ_c = 0.92 ± 0.03 D with the total dipole moment, μ, having a value of 4.14 ± 0.09 D.     

Improvement of the parametric method of the theory of vibronic spectra of polyatomic molecules: Absorption spectra and the structure of butadiene, hexatriene, and octatetraene in the excited state

The structure of the excited states and absorption spectra of butadiene, hexatriene, and octatetraene are calculated by the parametric method of the theory of vibronic spectra using models of the first-and second-order approximations. It is shown that these molecular models adequately reflect the molecular structure and allow one to predict quantitatively the shape and fine vibrational structure of the absorption spectra. When passing to the second-order approximation, only two additional (angular) parameters are used. These parameters are transferable in the series of polyenes. Compared to the first-order approximation model, the second-order approximation model more accurately takes into account the angular deformations of polyenes upon their excitation and describes the intensity distribution in the vibrational spectrum, including weak lines. In addition, the calculations also quantitatively predict spectral variations in the molecular series. The parametric method is more efficient for modeling polyatomic molecules in the excited states and their vibrational spectra compared to other semiempirical and ab initio methods.     

Determination of the Dipole Moment of O-18 Methanol by Microwave Stark Spectroscopy

In this paper we report accurate measurements of microwave (MW) frequencies for nine different transitions in the first four torsional states in the ground vibrational state of O-18 substituted methanol, for a wide range of applied dc electric field. The Stark-shifted frequencies were measured with accuracies of about ±10 kHz. The results were analyzed to deduce accurate dipole moment values for the four torsional states involved. Substantial variation of dipole moment was observed as a function of the torsional state. The zero field frequencies have been also determined with much better precision than known before. The dipole moment values for the torsional ground state have been determined to be μ_a= 0.8992(8) and μ_b= 1.4226(3) D. The dipole moment value increases with torsional excitation. These values will be useful for the evaluation of relative intensities of interstellar microwave and millimeter wave transitions and optically pumped far infrared laser lines.     

Modeling non-Lorentzian two-photon absorption line shape in dipolar chromophores

We present a new approach to modeling of homogeneous line shape in two-photon absorption (2PA) spectra of chromophores with large permanent dipole moment difference between the ground- and excited electronic states using numerical solution of stochastic two-level density matrix equation of motion. Good agreement with experimental 2PA line shapes is obtained for S₁←S₀ transition of Styryl 9 M, which allows us to estimate that the permanent dipole moment difference varies in this chromophore within the S₁←S₀ band in the range, Δμ=12-25 D.     

Stark effect measurements on the NaK molecule

In a newly built molecular beam apparatus we have measured permanent electric dipole moments of the B ¹ Π and X ¹ Σ ⁺ states of NaK to test the vibrational dependence of the dipole moment function as predicted by ab initio calculations by Aymar and Dulieu [J. Chem. Phys. 122, 204302 (2005)]. Four vibrational bands were studied, the dipole moment for the B ¹ Π decreases from 2.73(2) D for v = 3 to 1.99(2) D for v = 13. The vibrational dependence shows a fairly good agreement with theory, but the absolute values are lower than those from the calculation by 13%. The ground state dipole moment of 2.72(6) confirms the earlier result by Wormsbecher et al. [J. Chem. Phys. 74, 6983 (1981)].     

Theory of pressure-induced vibrational and rotational absorption of diatomic molecules at high temperatures

A derivation is given for the integrated absorption coefficient of pressure-induced pure rotational and vibrational transitions in binary collisions of homonuclear diatomic molecules of the same chemical species. The previously neglected effects of excited vibrational states, mechanical anharmonicity, and vibration-rotation interaction are taken into account to obtain more accurate absorption coefficients at high temperatures. In the region of the fundamental wave number the excited vibrational states make more of a contribution to the absorption than their relative population would lead one to expect.     

The microwave spectrum,structure, and dipole moment of propiolyl fluoride

The microwave spectrum of propiolyl fluoride has been observed in the frequency region 12.5–40 GHz. Rotational transitions have been assigned for the ground and two excited vibrational states of the normal isotopic species and for the ground vibrational state of the deuterated species. In each case, values for the rotational constants and centrifugal distortion constants have been obtained. The molecule has been shown to be planar and structural calculations suggest no anomalies in any of the internuclear parameters. Stark effect measurements have yielded a value of 2.98 ± 0.02 Debyes for the dipole moment.     

New all-optical method for measuring molecular permanent dipole moment difference using two-photon absorption spectroscopy

Stark effect, in combination with spectral hole burning and single-molecule spectroscopy, has been a fruitful technique to study permanent electric dipole moment of molecules in condensed phase. However, because measuring Stark shifts relies on external fields and narrow line- or hole-widths, the applicability of this method at ambient conditions required by most biological systems has remained limited. Here we demonstrate a new all-optical method for measuring the molecular dipole moment difference between ground and excited states using two-photon absorption (2PA) spectroscopy. We show that the value and orientation of the static dipole moment difference can be determined from the corresponding absolute 2PA cross-section. We use this new method to determine for the first time the strength of local electric field E_loc=0.1-1.0×10⁸ V/cm inside beta-barrel of Fruit series of red fluorescent proteins. Because our method does not rely on external field and is applicable in liquid solutions, it is well suited for the study of biological systems.     

Microwave spectrum of chlorine nitrate (ClNO3)

Microwave spectra of chlorine nitrate (³⁵ClNO₃ and ³⁷ClNO₃) in the ground and first excited vibrational states have been analyzed in detail. Rotational constants and centrifugal distortion parameters are reported for each species. The permanent electric dipole moment in ClNO₃ was found to have two components, μ_a = 0.72 ± 0.07 D and μ_b = 0.28 ± 0.02 D.     

Dipole moment function of carbonyl sulphide

Measurements are reported for the infra-red absorption intensity of some overtone and combination bands in carbonyl sulphide. These are interpreted with the aid of an anharmonic force field and some microwave Stark effect measurements on excited vibrational states to give the values for the dipole in the equilibrium configuration, p _e, and the linear and quadratic derivatives for the axial dipole component shown in table 4. These signs are absolute, being tied to the microwave Zeeman effect on isotopically substituted molecules [4].