Collisional excitation of Na-Rydberg atoms

The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered. The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as well as principal quantum number. Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002     

A novel study of charged carbon clusters using a tandem Van de Graaff accelerator

A conventional tandem Van de Graaff accelerator is used to produce charged carbon cluster beams. The unique capability of the method for studying highly charged clusters unaccessible to other methods of producing cluster beams is demonstrated.     

Niobium-93 MQMAS NMR spectroscopic study of alkali and lead niobates.

93Nb (I = 9/2) multiple-quantum magic-angle spinning (MQMAS) NMR spectra of a series of inorganic niobates have been measured. 93Nb MQMAS spectroscopy yields spectra with typically an order of magnitude higher resolution than that obtainable with 93Nb MAS spectroscopy and 93Nb dynamic-angle spinning (DAS) spectroscopy. For example, the full-width at half-maximums of the 93Nb resonances of LiNbO3 were 9 (MAS), 5.8 (DAS), and 0.7 kHz (MQMAS). Broadening of the 93Nb MAS and DAS spectra is due to the second-order quadrupolar and homonuclear dipolar interactions, respectively. The quadrupolar products (P(O)) and isotropic chemical shifts (delta(iso)) of the 93Nb resonances of LiNbO3, NaNbO3, PbNb2O6, Pb2Nb2O7, Pb3Nb2O8, Pb3Nb4O15, Pb3Nb4O13, and Pb1.83Nb1.71Mg0.29O6.39 were determined from MQMAS spectra and range from 13.6 to 26.8 MHz and from -951 to -1113 ppm, respectively. Resonances with relatively large quadrupolar coupling constants (> 30 MHz) were not observed using MQMAS spectroscopy, but were detected using nutation spectroscopy. The applicability and limitations of MQMAS spectroscopy in studying inorganic niobates containing multiple 93Nb resonances are addressed and compared with those of MAS, nutation, and DAS spectroscopies.     

Orientational order parameter studies on 3.Om and 3O.Om liquid crystals

Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/T_c) ^β, effective geometry parameter α_g and Vuks’ scaling factor S_C. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method.     

Metformin and glitazones: does similarity in biomolecular mechanism originate from tautomerism in these drugs?

This theoretical study attempts to find out similarity between metformin and glitazone class of antidiabetic drugs. It was found that some tautomeric forms of both metformin and thiazolidinedione ring of glitazones have similar molecular electrostatic potential (MESP) surface and may bind to a common complementary surface. Complexation and docking studies were also carried out in order to support this hypothesis. Copyright © 2007 John Wiley & Sons, Ltd.     

Rotational spectra of mono-substituted asymmetric C6H6-H2O dimers

This paper reports the assignment of the rotational spectra of the m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. The m = 1 progression was not identified or assigned for both ¹³CC₅H₆-H₂O and C₆H₅D-H₂O in the earlier work, though for the symmetric isotopomers (C₆H₆-H₂O/D₂O/H₂¹⁸O), they were identified [H.S. Gutowsky, T. Emilsson, E. Arunan, J. Chem. Phys. 99 (1993) 4883]. The m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O were split into two, unlike that of the parent C₆H₆-H₂O isotopomer. The splitting varied, somewhat randomly, with quantum numbers J and K. The m = 0 lines of ¹³CC₅H₆-H₂O had significant overlap with the m = 1 lines of the parent isotopomer, clouding proper assignment, and leading to an rms deviation of about 200 kHz in the earlier work. The general semi-rigid molecular Hamiltonian coupled to an internal rotor, described recently by Duan et al. [Y.B. Duan, H.M. Zhang, K. Takagi, J. Chem. Phys. 104 (1996) 3914], is used in this work to assign both m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. Consequently, the m = 0 fits for ¹³CC₅H₆-H₂O/D₂O have an rms deviation of only 4/7 kHz, comparable to experimental uncertainties. The fits for m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers have an rms deviation of about 200 kHz. However, it is of the same order of magnitude as that of the m = 1 state of the parent C₆H₆-H₂O dimer. The A rotational constants determined from the m = 0 fits for both ¹³CC₅H₆-H₂O and ¹³CC₅H₆-D₂O isotopomers are identical and very close to the C rotational constant for ¹³CC₅H₆. This provides a direct experimental determination for the C rotational constant of ¹³CC₅H₆, which has a negligible dipole moment.     

Elasticity-mediated self-organization and colloidal interactions of solid spheres with tangential anchoring in a nematic liquid crystal

Using laser tweezers, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with tangential surface anchoring. The interactions overcome the Brownian motion when the interparticle separation r-->p is less than 3 particle diameters. The particles attract when the angle theta between r-->p and the uniform far-field director n0 is between 0 degrees and approximately 70 degrees and repel when 75 degrees 相似文献   

Experimental studies on the microstructure and hardness of laser-treated steel specimens

An experimental investigation with 5 kW CW CO₂ laser system was carried out to study the effects of different laser and process parameters on the microstructure and hardness of carbon steel specimen with varying carbon percentage. The laser beam is allowed to scan on the surface of the work piece varying the power (1.1–2.5 kW) and traverse speed (6–15 mm/s) at two different spot sizes using TEM_01* mode laser beam. The most hardenable microstructure achieved in case of three grades of carbon steel and the most influencing parameter on the value of hardness are reported. Besides the above study, some multipass operations are also carried out to recommend an appropriate gap between consecutive passes.     

Thermodynamic parameters of N-(p-n-alkoxybenzylidene)-p-n-(butyloxyanilines), (nO.O4) liquid crystal compounds — A dilatometric study

Different thermodynamic parameters are estimated from volume expansion coefficient, α for a number of N-(p-n-alkoxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds in isotropic phase (at T_IN + 5 °C) and in liquid crystalline phases. The variation of different thermodynamic parameters with the alkoxy chain length in nO.O4 series and their variation with the temperature in individual liquid crystal compounds are discussed. The parameters like available volume (V_a), inter molecular free length (L_f) and molecular radius (M_r) are also computed from density, and refractive index for these nO.O4 compounds and the nature of molecular free length and molecular radius are analyzed and discussed.     

Estimation of anharmonic parameters, molecular radius, Mr and Beyer's non-linearity parameter, B/A in TBnA series

The thermodynamic parameters like Moelwyn-Hughes parameter (C₁), reduced molar volume (V^~), isochoric temperature coefficient of internal pressure (X), Huggin's parameter (F), Gruneisen parameter (Γ_p), isothermal microscopic Gruneisen parameter, Sharma parameter (S_o), fraction free volume (f) and (A^?) a dimensionless thermal parameter, etc and the Beyer's nonlinearity parameter (B/A) were deduced employing the thermal expansion coefficient derived from density data for the homologues series of compounds terephthalyidene-bis-p-n-alkyl anilines, TBnA with n = 5 to 10,12,14,16 and 18. Further, it is found that the variation of molecular radius, M_r increases with the increase of alkyl chain number, with a core radius of 4.78 Å and the increment for methylene unit is 0.086 Å . The results were discussed with the body of the data available.