The width of the rotational contour of vibrational and vibronic bands of complex molecules in the gas phase as a temperature indicator

From the independence of the contour of spectral density of the rotational (orientation) correlation function of a rigid molecular top of arbitrary symmetry on temperature in the frequency scale based on the reduced time of rotational orientation relaxation and from the near independence of the rotational contour of vibrational and vibronic absorption bands of dipole transitions in the same coordinates in a model of “regular diffusion” of the transition oscillator with a classically rotating rigid molecular top, it is suggested that it is possible to use the halfwidth of the contour for estimation of temperatures. Data are presented on the halfwidth of 48 contours of bands of A, B, and C types at this frequency for 12 compounds for a temperature range of from units to 500 degrees of absolute temperature measured experimentally and (for low temperatures) calculated by the quantum theory. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 312–317, May–June, 1997.     

Efficiency of the structure analysis of complex molecules in the gas phase by their optical rotation

It was shown in the dipole approximation of optical rotation that in the general case only in orientationally anisotropic vapors is the rotational force dependent on the intramolecular orientation of both the electric and magnetic dipole moments. Expressions relating the optical rotational force to the intramolecular orientation of these moments, the orientational distribution in an anisotropic ensemble, and the configuration of a measurement have been obtained. Calculated dependences of the rotational force on the intramolecular orientation of the magnetic moment at a fixed electric moment and “rotational force excitation spectra” obtained for different types of rigid asymmetric top molecules and rotational contours are presented. It is proposed to measure the intramolecular orientation of the electric and magnetic dipole moments with the use of the rotational force normalized to that detected in the case of observation at a “magic” angle to the direction of the exciting light electric vector. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 843–849, November–December, 1998.     

Conformal transitions of the laurdan molecule in the absorption and fluorescence spectra

The fluorescent probe molecule – laurdan (6-dodekanoil-2-dimetilamin naphthalene) – is investigated by experimental and quantum-chemical methods. The influence of the structure non-rigidity on the dipole moments, arrangement of energy levels, and distribution of charges in the laurdan molecule is studied. An optimized structure is obtained and analyzed by the molecular dynamics method. Several structures with different rotation angles of the dimethylamino group are investigated, for which energy, oscillator forces, and nature of electron states are calculated. Fluorescence spectra of the laurdan molecule in an inert solvent are interpreted. Centers of possible interaction of the molecule with a proton-donor solvent are established. Rate constants of radiative and nonradiative processes and quantum fluorescence yields of the examined probe are calculated.     

Lability of the Configuration of Free Complex Molecules and Polarized Luminescence

We compare the sensitivity of the degree of polarization of integral fluorescence for excitation by light with a spectral width larger than the width of the rotating loop or only in the Qbranch of the rotating loop to a change in the principal moment of inertia (rotational constants) of complex molecules in vapors. It is shown that the sensitivity depends on the degree of asymmetry of the molecular top and the intramolecular orientation of the dipole transition moments. Improvement of the symmetry of the asymmetric top leads to an increase in the sensitivity to at least one of the rotational constants. Such effects are also noted for the sensitivity of the period of the rotational quantum echo to a change in the rotational constants.     

Revisit of rotational motion of axial poly-atomics by molecular dynamics simulation and group theory: liquid benzene at 298, 365, 432, 498, 562 K

The paper reports quantitative physical aspects of the overall rotational motion of axially symmetric poly-atomics on the example of liquid benzene at five temperatures between 298 and 562?K on the basis of the group-theoretical approach proposed by B. Keller and F. Kneub?hl in Helv. Phys. Acta 45,1127 (1972), with a database generated by molecular dynamics simulation of ensemble-averaged orientational fluctuations. It is shown that (i) benzene rotates by a Markov process around an average, in-frame moving rotation axis and (ii) that numerous reported orientational correlation results that claim to display the rotational motion of the molecule, are nevertheless now to be considered irrelevant to their promulgated aim because their analyses omitted to account for the simultaneous inclination motion, as well as its particular time scale, of the average direction of the singular average molecular rotation axis of a benzene molecule.     

Spectra of the <Emphasis Type="Italic">gauche</Emphasis>-conformer of isopropyl alcohol in the millimeter and submillimeter wavelength regions

The spectrum of isopropyl alcohol in the millimeter region was recorded using a hybrid radio-spectrometer. A total of 1278 rotational and vibration-rotational transitions of its gauche-conformer were identified. Rotational constants and quartic centrifugal constants were refined. Sextic centrifugal constants and all six internal rotation constants were determined. The tunnel splitting parameter was refined. The reduced Hamiltonian of internal rotation is used for the first time in full format and describes sufficiently well the vibration-rotational spectrum of the gauche-conformer of isopropyl alcohol, which is complicated by internal rotation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 659–665, September–October, 2008.     

Selective excitation of the molecular rotational wave packet by two time-delayed laser pulses

In this paper, we investigate the control of the molecular wave packet of a linear molecule by two femtosecond laser pulses. It is shown that the odd and the even rotational wave packets created by a single laser pulse can be selectively excited by accurately controlling the time delay of another laser pulse. By inserting the peak of the second laser pulse at the position of maximum or minimum value around quarter or three quarter rotational period of the slope curve with odd (or even) rotational wave packet contribution that is created by the first laser pulse, the odd rotational wave packet can be enhanced (or suppressed) while the even rotational wave packet is suppressed (or enhanced). As a result, the molecular alignments around quarter and three quarter rotational periods can be obtained. Moreover, it is also shown that by inserting the second laser pulse around the quarter or three quarter rotational periods, the changes in the maximum degree of the molecular alignment for the odd and the even rotational wave packet contributions are consistent with their corresponding slope curves at these positions.     

Nuclear spin–spin constants,rotational g factor and susceptibility of sulphur hexafluoride

Following our previous study on spin–rotation and shielding constants of the SF₆ molecule, the rotational g factor and the magnetic susceptibility are calculated here, using ab initio methods to evaluate the electronic contribution to the nuclear hyperfine constants, and compared with experimental results. It is shown, for the first time, that the electronic component of the rotational g factor is proportional to a constant, which is given by a sum over electronic states. We also evaluate for the SF₆ molecule the indirect, or electron-coupled spin–spin interaction, theoretically described by Ramsey, and show that it gives non-negligible corrections to direct coupling constants d ₁ and d ₂. The contributions of the terms included in this interaction (DSO, PSO, SD and FC) are also analysed.     

Influence of isovalent substitutions on absorption spectra of orthoferrities

The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on the optical absorption of orthoferrites that are promising for magnetooptics is studied. Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072, Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997.     

Collisional Relaxation of Luminescence Anisotropy in Rarefied Gases in the Condensed Phase

The orientational relaxation of optically induced anisotropy in rarefied gases and at a damped rotation has been investigated. It has been found that the anisotropy relaxation in rarefied gases is described by a reduced kinetic equation depending only on free rotation integrals. The behavior of the integral anisotropy of luminescence for free symmetric and asymmetric top molecules has been elucidated. The law of luminescence depolarization has been obtained for asymmetric top molecules in the Gordon J-diffusion model. It represents the sum of two Stern–Volmer-type dependences, whose relative contribution is determined by the orientation of the dipole moments of transitions with absorption and emission of light in the molecular coordinate system and by the principal moments of inertia of the molecular top. It has been established that in the limit of a strongly damped rotation, kinetic equations of the general form reduce to equations of rotational diffusion. A number of modified diffusion equations correctly describing the contribution of inertial effects to the orientational relaxation of anisotropy have been obtained.     

Determining if a System is Heterogeneous: The Analysis of Single Molecule Rotational Correlation Functions and Their Limitations

Single molecule spectroscopy can be utilized to measure distributions of individual molecular properties that may be averaged out in the ensemble measurement. For example, complex dynamics in disordered systems can be investigated by observing single molecule rotations via fluorescence spectroscopy. The rotational time of a single transient can be calculated from the correlation function of the reduced linear dichroism signal which fluctuates over time as the molecule reorients in its surroundings. Distributions of rotational time constants can be used to characterize the heterogeneity of molecular environments in the material. This paper reviews some theoretical studies on (1) the high numerical aperture effects on the final correlation function, and how it can be related to optical anisotropy decays in a bulk measurement; (2) the statistical errors resulting from the finite observation length that will propagate into distributions of rotational times. These lead to the discussions on how to interpret correctly the distribution of properties measured from a set of single molecule data, and to determine if in fact the system is heterogeneous.     

Quantum-Chemical Calculations of the Excited Electronic States of the Prodan Molecule and Its Complexes in Water

A quantum-chemical calculation of the prodan molecule and its complexes in water for the geometry of the ground and fluorescent states is carried out. To describe the fluorescent state, changes in the electronic state (population) on bonds and atoms during transition of the molecule into an excited state are taken into account. A model of interaction of the prodan molecule with a polar proton-donor solvent (water) is suggested. It is shown that interaction with the ionic forms (H₃O₊ provides an explanation for the sensitivity of prodan to the solvent (displacement of the fluorescence bands). The nature of the electronic excited states of the prodan molecule and its complexes has been investigated. The constants of the rates of radiative and nonradiative processes and the fluorescence quantum yields have been calculated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 330–334, May–June, 2005.     

Analysis of torsional vibrations of an ethane molecule

Based on the solution for the Mathieu equation, we obtained wave functions for the internal rotation of an ethane molecule that satisfy the symmetry properties of the group G₃₆. We calculated the frequency of the principal torsional transition (273 cm⁻¹). The types of symmetry of the energy levels and transition probabilities in IR and Raman spectra are determined. We note drawbacks of divisible permutable-inverse nuclear groups and the groups of molecular symmetry associated with their construction, as well as difficulties that appear when equivalent rotations are used. The possibility of avoiding the application of an extended group is indicated. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 26–31, January–February, 1997.     

The C2II-X2Σ system of SrF molecule

The spectrum of the C²II-X² Σ system of SrF molecule has been investigated under high resolution. The rotational structure in the (0, 0) band has been analysed and the rotational constants for the C²II state have been obtained. The vibrational analysis of this system has been carried out using the band heads from the high resolution spectrogram and also the band origins and the precise vibrational constants have been reported for both the participating states.     

Active manipulation of the selective alignment by two laser pulses

This paper solves numerically the full time-dependent Schrdinger equation based on the rigid rotor model, and proposes a novel strategy to determine the optimal time delay of the two laser pulses to manipulate the molecular selective alignment. The results illustrate that the molecular alignment generated by the first pulse can be suppressed or enhanced selectively, the relative populations of even and odd rotational states in the final rotational wave packet can be manipulated selectively by precisely inserting the peak of the second laser pulse at the time when the slope for the alignment parameter by the first laser locates a local maximum for the even rotational states and a local minimum for the odds, and vice versa. The selective alignment can be further optimised by selecting the intensity ratio of the two laser pulses on the condition that the total laser intensity and pulse duration are kept constant.     

Spectral energy characteristics of 6,γ- and 7,γ-dimethyl ethers of chlorine 6 in water-alcohol solutions

Absorption spectra and dispersion of optical rotation (DOR) are measured for monomers of 6,γ- and,7,γ-dimethyl ethers of chlorin e₆ (Ch-6,γ-DME and Ch-7,γ-DME) in 96% ethanol and for associates of them that are polymers and colloidal particles. The optical activity of Ch-6,γ-DME monomers is higher than that of Ch-7,γ-DME monomers, which is linked with more pronounced distortion of the molecular macrocycle for Ch-6,γ-DME in the γ-C₆ local region. The structural and energy parameters of dimeric unit cells of Ch-6,γ-DME and Ch-7,γ-DME polymers are discussed from the standpoint of the Davydov-Tinoko exciton theories. Longwave absorption spectra and DOR are resolved into individual components with the aid of a modified Alentsev-Fock method. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 331–337, May–June, 1999.     

量子干涉效应中干涉角和散射角的研究

利用波恩近似理论对双原子激发态转动传能进行了剖析,更深入的研究了原子分子碰撞过程中量子干涉效应相关信息．利用各项异性相互作用势和直线轨迹近似建立了新的量子干涉模型,讨论了原子与分子碰撞时散射角和微分干涉角的关系,得到了干涉角和各向异性参数及转动量子数的关系．     

Kinetic theory of rotating molecule interaction with a solid surface

A kinetic theory of interaction between molecules with rotational degrees of freedom and a solid surface for arbitrary ratios among the times of molecule rotation, flight through the region of surface forces, and relaxation of a molecular ensemble due to phonons has been developed. A kinetic equation for an ensemble of molecules residing in the field of surface forces has been derived from the equation for the one-particle distribution function of molecules by averaging it along the dynamical trajectories in the region of surface force action. A simple analytic expression for the probability of trapping a molecule with rotational degrees of freedom has been obtained. Experimental data on rotational cooling and rotational polarization of desorbed molecules are discussed. Zh. éksp. Teor. Fiz. 113, 1350–1363 (April 1998)     

Microwave spectrum ofcis 3-fluorophenol

The microwave spectrum ofcis 3-fluorophenol involving rotational states up toJ=28 has been observed and analysed in the frequency range 23–25 GHz in the ground vibrational state at room temperature. Analysis yields three rotational and five quartic centrifugal distortion constants. A tentativer ₀ structure has been proposed satisfying the observed rotational constants. The small value of the inertia defect Δ=0·07 confirms the planarity of the conformer.     

The microwave spectrum and quadrupole coupling in tricarbonyl(methylcyclopentadienyl) manganese

The rotational spectrum of tricarbonyl(methylcyclopentadienyl) manganese has been recorded in the range from 1–23 GHz using an FTMW spectrometer working on a molecular beam. This spectrum is assigned for the first time, yielding the rotational constants of the molecule and quartic centrifugal distortion constants. The fine structure due to the quadrupole interaction of the ⁵⁵Mn nucleus could be solved and gave the quadrupole coupling tensor (which is compared with that of tricarbonyl(cyclopentadienyl)manganese, and the spin-rotation constants. An additional splitting of a few kHz, which could be observed for some transitions, is interpreted as arising from the internal rotation of the methyl group.