An ab Initio Study of the ÃΠ State and the ÃΠ←X?Σ Electronic Transition of MgNC

We use the RENNER program system (see, for example, P. Jensen, G. Osmann, and P. R. Bunker, in “Computational Molecular Spectroscopy” (P. Jensen and P. R. Bunker, Eds.), Wiley, Chichester, 2000, and references therein) to make a detailed calculation of the rovibronic energies in the first excited electronic state, òΠ, of the MgNC radical. This calculation is based on ab initio data (supplemented here with points for larger bending displacements from linearity) calculated at the level of MR-SDCI(+Q)/[TZ3P+f(Mg), aug-cc-pVQZ (N and C)] by T. E. Odaka, T. Taketsugu, T. Hirano, and U. Nagashima (J. Chem. Phys.115, 1349-1354 (2001)). These authors employed ab initio derived spectroscopic constants to calculate vibronic energies using perturbation expressions (J. T. Hougen and J. P. Jesson, J. Chem. Phys.38, 1524-1525 (1963)), and their results suggested that an observed vibronic band belonging to the òΠ←X?²Σ⁺ electronic transition (R. R. Wright and T. A. Miller, J. Mol. Spectrosc.194, 219-228 (1999)) should be reassigned. The present work confirms this conclusion, which is further substantiated by the rotational structures calculated in the vibronic states and by Franck-Condon theory predicting relative intensities.     

The calculation of active Raman modes of α-quartz crystal via density functional theory based on B3LYP Hamiltonian in 6–311+G(2d) basis set?

We obtained an approximation of the force field of ??-quartz crystal using a new idea of applying density functional theory [J Purton, R Jones, C R A Catlow and M Leslie, Phys. Chem. Minerals 19, 392 (1993)]. Our calculations were based on B3LYP Hamiltonian [A N Lazarev and A P Mirgorodsky, Phys. Chem. Minerals 18, 231 (1991)] in 6?311+G(2d) basis set for H₁₆Si₇O₆ cluster and included a unit cell of the lattice. The advantage of our method is the increase in the speed of calculations and the better adaption of simulation results with the experimental data.     

Remarks on a recent article of Ch. Obcemea and E. Brändas on the theory of subdynamics

In a recent paper on the theory of subdynamics, Ch. Obcemea and E. Brändas (Ann. Phys (N.Y.)151 (1983), 383–430) claimed to correct a recently published result (M. Courbage, J. Math. Phys.23 (1982), 646, 652). It is shown that this criticism is unfounded. Some additional remarks are made.     

Theoretical transition probabilities for the OH meinel system

An electric dipole moment function (EDMF) for the X²Π ground state of OH based on the complete-active-space self-consistent-field plus multi-reference-singles-plus-double-excitation configuration-interaction procedure using an extended Slater basis is reported. This EDMF and the recently published MCSCF(7)-self-consistent electron pairs (SCEP) EDMF of H-J. Werner, P. Rosmus, and E-A. Reinsch [J. Chem. Phys. 79, 905–916 (1983)] (WRR) are critically compared with the “experimentally” derived EDMF. Einstein coefficients calculated with both theoretical EDMFs are substantially different than those reported by F. H. Mies [J. Mol. Spectrosc. 53, 150–188 (1974)] based on the EDMF of W. J. Stevens, G. Das, A. C. Wahl, D. Neumann, and M. Krauss [J. Chem. Phys. 61, 3686–3699 (1974)]. By shifting the WRR EDMF by 0.03 Bohr to larger r, it is possible to reproduce the accurate experimental value for the difference in dipole moments between the v = 0 and v = 1 levels measured using the molecular beam electric resonance technique. Following the theory of Mies (except that Hill and Van Vleck's intermediate coupling approximation is used), revised Einstein coefficients are tabulated for Δv = v′ – v″ ranging from the fundamental transition, Δv = 1 to the Δv = 5 overtone for v′ = 1–9, and J′ = 0.5–15.5 using the “shifted” WRR EDMF. Theoretical emission spectra are also presented, and the potential for OH involvement in the surface glow of space vehicles is briefly discussed.     

A Theoretical Study of MgNC and MgCN in the X?Σ Electronic State

The MgNC radical was the first Mg-containing species to be observed in interstellar space. This fact has stimulated considerable spectroscopic interest in this molecule, and in its isomer MgCN, but nevertheless the only rotationally resolved spectroscopic data presently available for X?²Σ⁺ MgNC comprise the rotational spectrum (K. Kawaguchi et al., 1993, Astrophys. J.406, L39-L42; K. Ishii et al., 1993, Astrophys. J.410, L43-L44; M. A. Anderson and L. M. Ziurys, 1994, Chem. Phys. Lett.231, 164-170; E. Kagi et al., 1996, J. Chem. Phys.104, 1263-1267; E. Kagi and K. Kawaguchi, J. Mol. Spectrosc. 2000, 199, 309-310) together with a few vibronic bands, all originating in the vibronic ground state and belonging to the òΠ←X?²Σ⁺ electronic transition (R. R. Wright and T. A. Miller, 1999, J. Mol. Spectrosc.194, 219-228). For MgCN, only the rotational spectrum in the vibrational ground state is known (M. A. Anderson, T. C. Steimle, and L. M. Ziurys, 1994, Astrophys. J.429, L41-L44). We report here potential energy surfaces calculated by the Averaged Coupled-Pair Functional (ACPF) method with TZ3P+f (Mg), TZ2P+f(N,C) basis sets including core-valence correlation due to the Mg 2s and 2p electrons. The ab initio results are used for determining the standard spectroscopic constants of X?²Σ⁺ MgNC and MgCN. Also, we report variational calculations of the rotation-vibration energies, and variational simulations of the lowest rotation-vibration bands, carried out with the MORBID program system (P. Jensen, 1988, J. Mol. Spectrosc.128, 478-501). We hope that our theoretical results will encourage and facilitate further characterization of X?²Σ⁺ MgNC and MgCN by high-resolution spectroscopy.     

Scattering of Stark-decelerated OH radicals with rare-gas atoms

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X²Π_3/2, J = 3/2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D₂ as a function of the collision energy between ～70 cm^?1 and 400 cm^?1. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by coupled channel scattering calculations based on accurate ab initio potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, G. Meijer, Science 313, 1617 (2006)], Ar [L. Scharfenberg, J. K?os, P.J. Dagdigian, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Chem. Chem. Phys. 12, 10660 (2010)], He, and D₂ [M. Kirste, L. Scharfenberg, J. K?os, F. Lique, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Rev. A 82, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.     

Electric anharmonicity in XY3 pyramidal molecules: The dipole moment function of 14NH3 and 15NH3

This paper is concerned with the determination of the shape of the electric dipole moment function of a pyramidal XY₃ molecule with a low barrier to inversion over a wide range of values for the inversion coordinate. The effective inversion-rotation Hamiltonian [V. ?pirko, J. M. R. Stone, and D. Papou?ek, J. Mol. Spectrosc.60, 159–178 (1976)] is used to explain the anomalous vibrational dependence of the electric dipole moment of ¹⁴NH₃ [F. Shimizu, J. Chem. Phys.52, 3572–3576 (1970)], and of ¹⁵NH₃ [B. J. Orr and Takeshi Oka, J. Mol. Spectrosc.66, 302–313 (1977)]. The experimental data of Orr and Oka are used to fit the μ_z component of the total dipole moment function and the fitted function is used to predict the transition moments in the nν₂ inversion sequence of ¹⁴NH₃ and ¹⁵NH₃. To illustrate the measure of the rotational dependence of the transition moments, two examples, involving ground and excited (v₂ = 1) states, are also presented.     

Processing of heteronuclear NMR relaxation data with the new software DASHA

The new program DASHA is an efficient implementation of common data processing steps for the protein internal dynamic analysis. The “model-free” parameters and their uncertainties (Lipari G., Szabo A.: J. Am. Chem. Soc.104, 4546–4559 (1982) can be calculated from an arbitrary combination of experimental data sets (i.e. heteronuclear¹H?¹⁵N or¹H?¹³C relaxation times and NOE values at different spectrometer frequencies). Anisotropy of the molecular rotational diffusion could be also taken into account without introduction of the new adjustable parameters into the spectral density functionJ(ω), provided the structure of the molecule is known. Parameters of chemical (conformational) exchange can be estimated from the CPMG spin-lock frequency dependences (Bloomet al.: J. Chem. Phys.42, 1615–1624 (1965); Orekhovet al.: Eur. J. Biochem.219, 887–896 (1994). The program can be used both in the interactive and batch modes. It has sophisticated PostScript plotting facilities.     

Reanalysis of the D → X fluorescence spectrum of I2

The uv fluorescence spectrum of I₂ excited by iodine atomic radiation at 1830 Å is photographed and analyzed using a direct least-squares-fitting method with consistency constraints on the centrifugal distortion constants. The analysis confirms Verma's [J. Chem. Phys.32, 738–749 (1960)] prior analysis of this spectrum and yields improved molecular constants for v = 0–99 of the X state and $\text{v ? 204–208}$ of the D state.     

Monte Carlo Simulation of Hard Hyperspheres in Six,Seven and Eight Dimensions for Low to Moderate Densities

The pair correlation function of hard hyperspheres in six, seven and eight dimensions is obtained from Monte Carlo simulations. The value of the pair correlation function at contact is compared with the results from molecular dynamics calculations and a variety of theoretical approaches. Remarkably good agreement is found with the simple, closed-form equations of Y. Song, E. A. Mason and R. M. Stratt, J. Phys. Chem., 93:6916–6919 (1989). The Monte Carlo results for the equation of state are compared with the theoretical expressions of M. Baus and J. L. Colot, Phys. Rev. A, 36:3912 (1987), M. Luban and J. P. J. Michels, Phys. Rev A, 41:6796 (1990), and high order virial expansions. In addition, in seven dimensions, comparisons are made with the exact PY solution provided by M. Robles, M. L. de Haro and A. Santos, J. Chem. Phys., 120:9113 (2004). Very good agreement was observed between theory and computer simulation in all dimensions.     

New N2+Electronic States in the Region of 23–28 eV

Threshold photoelectron spectra of N₂⁺were measured between 23.4 and 27.6 eV with high resolution and high intensity by using the penetrating field technique and synchrotron radiation. Five vibrational progressions were observed. The first of these progressions was theC²Σ_u⁺state. The second progression was identified as the transition to the second state of²Π_gsymmetry found by P. Baltzer, M. Larsson, L. Karlsson, B. Wannberg, and M. Carlsson (1992.Phys. Rev. A46,5545). The third progression, which was discovered by F. Merkt and P. M. Guyon (1993.J. Chem. Phys.99,3400), can be designated as the²Σ_u⁻state by comparison with previous theoretical study (E. W. Thulstrup and A. Andersen, 1975.J. Phys. B8,965). The fourth and fifth progressions were designated as the²Δ_uand 2²Π_ustates by similar comparison with previous theories.     

Electronic transition dipole moment functions for transitions among the twenty-six lowest-lying states of Li2

Ab initio electronic transition dipole moment functions are calculated for all dipole-allowed transitions among the 26 states of Li₂ treated by D. D. Konowalow and J. L. Fish (Chem. Phys. 77, 435–448 (1983); Chem. Phys. 84, 463–475 (1984)). Many of the moments exhibit interesting behavior due to charge transfer or ion pair character. Comparisons are made with existing empirical and theoretical determinations of the 1¹Σ_u⁺-1¹Σ_g⁺ and 1¹Π_u-1¹Σ_g⁺ transition moments. The positions of a number of satellite bands are predicted from the potential energy difference curves.     

Single-oscillator model and determination of optical constants of spray pyrolyzed amorphous SnO<Subscript>2</Subscript> thin films

It has recently been shown that growth of a multilayer structure with one or more delta-layers at high temperature leads to spreading and asymmetrization of the dopant distribution [see, for example, E.F.J. Schubert, Vac. Sci. Technol. A. 8, 2980 (1990), A.M. Nazmul, S. Sugahara, M. Tanaka, J. Crystal Growth 251, 303 (2003); R.C. Newman, M.J. Ashwin, M.R. Fahy, L. Hart, S.N. Holmes, C. Roberts, X. Zhang, Phys. Rev. B 54, 8769 (1996); E.F. Schubert, J.M. Kuo, R.F. Kopf, H.S. Luftman, L.C. Hopkins, N.J. Sauer, J. Appl. Phys. 67, 1969 (1990); P.M. Zagwijn, J.F. van der Veen, E. Vlieg, A.H. Reader, D.J. Gravesteijn, J. Appl. Phys. 78, 4933 (1995); W.S. Hobson, S.J. Pearton, E.F. Schubert, G. Cabaniss, Appl. Phys. Lett. 55, 1546 (1989); Delta Doping of Semiconductors, edited by E.F. Schubert (Cambridge University Press, Cambridge, 1996); Yu.N. Drozdov, N.B. Baidus', B.N. Zvonkov, M.N. Drozdov, O.I. Khrykin, V.I. Shashkin, Semiconductors 37, 194 (2003); E. Skuras, A.R. Long, B. Vogele, M.C. Holland, C.R. Stanley, E.A. Johnson, M. van der Burgt, H. Yaguchi, J. Singleton, Phys. Rev. B 59, 10712 (1999); G. Li, C. Jagadish, Solid-State Electronics 41, 1207 (1997)]. In this work analytical and numerical analysis of dopant dynamics in a delta-doped area of a multilayer structure has been accomplished using Fick's second law. Some reasons for asymmetrization of a delta-dopant distribution are illustrated. The spreading of a delta-layer has been estimated using example materials of a multilayer structure, a delta-layer and an overlayer.     

Fluorescence Spectroscopic Properties Analysed within the Extended Förster Theory with Application to Biomacromolecular Systems

The extended Förster theory (EFT) of electronic energy transport accounts for translational and rotational dynamics, which are neglected by the classical Förster theory (FT). EFT has been developed for electronic energy transfer within donor-acceptor pairs [Isaksson, et al, Phys. Chem. Chem. Phys., 9, 1941(2007)] and donor-donor pairs [Johansson, et al, J. Chem. Phys., 105, 10896 (1996); Norlin, et al, Phys. Chem. Chem. Phys., 10, 6962(2008)]. For donors that exhibit different or identical non-exponential fluorescence relaxation within a donor-donor pair, the process of reverberating energy migration is reversible to a higher or lower degree. Here the impact of the EFT has been studied with respect to its influence on fluorescence quantum yields, fluorescence lifetimes as well as depolarisation experiments. The FT predicts relative fluorescence quantum yields which usually agree with the EFT within experimental accuracy, however, substantial deviations occurs in the steady-state and in particular the time-resolved depolarisation data.     

The effects of the N atom collective Lamb shift on single photon superradiance

The problem of single photon collective spontaneous emission, a.k.a. superradiance, from N atoms prepared by a single photon pulse of wave vector k₀ has been the subject of recent interest. It has been shown that a single photon absorbed uniformly by the N atoms will be followed by spontaneous emission in the same direction [M. Scully, E. Fry, C.H.R. Ooi, K. Wodkiewicz, Phys. Rev. Lett. 96 (2006) 010501; M. Scully, Laser Phys. 17 (2007) 635]; and in extensions of this work we have found a new kind of cavity QED in which the atomic cloud acts as a cavity containing the photon [A.A. Svidzinsky, J.T. Chang, M.O. Scully, Phys. Rev. Lett. 100 (2008) 160504]. In most of our studies, we have neglected virtual photon (“Lamb shift”) contributions. However, in a recent interesting paper, Friedberg and Mannassah [R. Friedberg, J.T. Manassah, Phys. Lett. A 372 (2008) 2514] study the effect of virtual photons investigating ways in which such effects can modify the time dependence and angular distributions of collective single photon emission. In the present Letter, we show that such virtual transitions play no essential role in our problem. The conclusions of [M. Scully, E. Fry, C.H.R. Ooi, K. Wodkiewicz, Phys. Rev. Lett. 96 (2006) 010501; M. Scully, Laser Phys. 17 (2007) 635; A.A. Svidzinsky, J.T. Chang, M.O. Scully, Phys. Rev. Lett. 100 (2008) 160504] stand as published. However, the N atom Lamb shift is an interesting problem in its own right and we here extend previous work both analytically and numerically.     

Effects of next-nearest-neighbor hopping interaction on polaron excitations in pernigraniline-base

The role of next-nearest-neighbor hopping interaction in determining the band structures and lattice configurations of combined polarons in pernigraniline-base polymer is explored on the basis of the Baranowski-Büttner-Voit (BBV) model. Numerical calculations show that the valence band extends to a larger range while the conduction band acts to the contrary, as the strength of the next-nearest-neighbor hopping interaction increases. The width of the Peierls gap and the number of the bound states trapped in have almost no changes. If the coupling strength β<0.15, the transition energy from the lower gap level to the higher one for a combined electron-polaron matches the long-lived 1.5 eV photoinduced absorption peak [J.M. Leng, R.P. McCall, K.R. Cromack, Y. Sun, S.K. Manohar, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. B 48 (1993) 15719], and also supports the high temperature dispersion in the thermally stimulated depolarization current (TSDC) experiment [A.N. Papathanassiou, J. Grammatikakis, S. Sakkopoulos, E. Vitoratos, E. Dalas, J. Phys. Chem. Solids 63 (2002) 1771]. For a combined hole-polaron, new shallow level emerges when β∼0.12.     

A Theoretical Study of AtildeΠ MgCN

We use the RENNER program system (see, for example, P. Jensen, G. Osmann, and P. R. Bunker, in “Computational Molecular Spectroscopy” (P. Jensen and P. R. Bunker, Eds.), Wiley, Chichester, 2000, and references therein) to make a detailed calculation of the rovibronic energies in the first excited electronic state, òΠ, of the MgCN radical. This calculation is based on ab initio data computed at the MR-SDCI(+Q)/[TZ3P+f (Mg), aug-cc-pVQZ (N and C)] level of theory. We have also obtained the standard spectroscopic constants and have used these to calculate vibronic energies from perturbation expressions (J. T. Hougen and J. P. Jesson, J. Chem. Phys.38, 1524-1525 (1963)); these results are compared to those computed with RENNER. It is shown that for MgCN, the perturbation theory is dilapidated due to Fermi resonances. No spectra involving the Ã²Π electronic state of MgCN have been observed. To assist such observations, we have calculated Franck-Condon factors for some of the vibronic bands in the òΠ←Xtilde;²Σ⁺ electronic transition.     

A quasi-classical trajectory study of the Cl + H<Subscript>2</Subscript> (D<Subscript>2</Subscript>) reaction on a new BW3 potential energy surface

Molecular reaction dynamics of Cl + H₂ (D₂) has been studied on the latest analytical potential energy surface called BW3 using the Monte Carlo quasi-classical trajectory method. Excitation functions, differential cross sections and angular distributions of HCl and DCl products have been calculated. The excitation functions of the Cl (²P_3/2) + n-H₂ and Cl(²P_3/2) + n-D₂ reactions are also studied. The results are compared with those of quasi-classical trajectory [M. Alagia et al.: Phys. Chem. Chem. Phys. 2 (2000); F. J. Aoiz et al.: J. Phys. Chem. 100 (1996)], quantum mechanical (QM) calculations [F. J. Aoiz et al.:J. Chem. Phys. 115 (2001)] and experimental data [S. H. Lee et al.: J. Chem. Phys. 110 (1999); F. Dong et al.: J. Chem. Phys. 115 (2001)]. Discussions are given to some new results.     

The bulk modulus and its pressure derivative for 18 metals

Volume compression data of Vaidya and Kennedy [J. Phys. Chem. Solids31, 2329 (1970)] have been used to recalculate the isothermal bulk moduli and their pressure derivatives and to compare various equations of state.     

HD structural isotope effect in hydrogen-bonded 2-aminoethanol

The microwave spectra of the d₃ species of intramolecularly hydrogen-bonded 2-aminoethanol (ODCH₂CH₂ND₂) as well as the d₃-O¹⁸, d₃-N¹⁵ and three d₂ isotopic forms have been studied. The r_s O-(D)?N distance of 2.8027(5) Å in the d₃ species is 0.0058(7) Å shorter than the O-(H)?N distance found earlier for the d₀ species (R. E. Penn and R. F. Curl, Jr., J. Chem. Phys.55, 651–658 (1971)). The anomalous r_s structural parameters $\text{r}\text{OH = 1.14}\text{A}\text{?}$ and ∠COH = 103.7°, when corrected for the systematic error caused by the O?N “shrinkage” upon deuteration, become 1.00 Å and 108°, respectively.