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The rotational spectrum of the hetero dimer comprising doubly hydrogen-bonded formic acid and acetic acid has been recorded between 4 and 18 GHz using a pulsed-nozzle Fourier transform microwave spectrometer. Each rigid-molecule rotational transition is split into four as a result of two concurrently ongoing tunneling motions, one being proton transfer between the two acid molecules, and the other the torsion/rotation of the methyl group within the acetyl part. We present a full assignment of the spectrum J = 1 to J = 6 for the ground vibronic states. The transitions are fitted to within a few kilohertz of the observed frequencies using a molecule-fixed effective rotational Hamiltonian for the separate A and E vibrational species of the G12 permutation-inversion symmetry group. Interpretation of the motion problem uses an internal-vibration and overall-rotation angular momentum coupling scheme and full sets of rotational and centrifugal distortion constants are determined. The tunneling frequencies of the proton-transfer motion are measured for the ground A and E methyl rotation states as 250.4442(12) and -136.1673(30) MHz, respectively. The slight deviation of the latter tunneling frequency from being one half of the former, as simple theory otherwise predicts, is due to different degrees of mixing in wavefunctions between the ground and excited states. [ABSTRACT FROM AUTHOR]

We present the first recording of the high-resolution spectrum of an induced chiral dimer. Three conformers of the induced chiral dimers of ethanol have been observed using a pulsed molecular-beam Fourier transform microwave spectrometer. The rotational constants of the normal isotopomers of the three species have been determined to be (a) A=5113.826(5), B=1329.7214(4), and C=1257.5151(3) MHz, (b) A=5086.459(5), B=1316.6508(4), and C=1243.6329(4) MHz, and (c) A=4851.608(5), B=1369.7558(6), and C=1243.4184(4) MHz. The observed species have been assigned to calculated structures via Kraitchman double substitution analyses and ab initio calculations. The Kraitchman analyses and the fitted centrifugal distortion parameters suggest that the deuterium bond is significantly stronger than the hydrogen bond in the dimers of ethanol. [ABSTRACT FROM AUTHOR]

The complexes between trifluoroacetic acid and water studied by means of pulsed nozzle Fourier transform microwave spectroscopy which were observed to exhibit hydrogen-bonded ring structures are reported.

Infrared absorption spectra for molecular beams of Ne·OCS have been observed with a diode laser for the vibrational transition near 2062 cm-1 correlating with the monomer ν3 mode. The linewidths were ∼150 MHz (FWHM), giving rotationally resolved spectra and allowing the upper and lower vibrational state A, B, and C rotational constants to be determined along with the frequency of the band origin. No broadening in excess of that expected from Doppler effects and laser linewidth was observed, setting a lower limit of 10-9 s on the lifetime of the upper state. Rotational transitions for the vibrational ground state were observed by microwave–infrared double resonance experiments. The ∼150 kHz linewidths in these experiments increased the precision of the rotational constants and permitted the quartic centrifugal distortion constants for the ground state to be determined. The effective structure of the Ne·OCS complex was calculated from the rotational constant data. The vibrational frequency and structural results are discussed in relation to similar work on other rare gas–OCS complexes. [ABSTRACT FROM AUTHOR]

Studies the spectroscopy and structure of the open-shell complex O[sub 2]-N[sub 2]O. Use of a molecular beam diode laser absorption spectrometer in the study; Analysis of the spectrum; Analysis of the structure; Effective structure of the complex; Inertial defect; Motion of the oxygen molecule; Intermolecular potential.

Presents an effective Hamiltonian for the analysis of the high-resolution spectra of open-shell van der Waals complexes containing the oxygen molecule. Rotational energy levels; Nonzero matrix elements of the Hamiltonian; Notation used to describe the energy levels.

Microwave and infrared spectra of the open-shell complex ArNO2 have been recorded. The microwave spectrum (6–18 GHz) consisted solely of the a-type transitions 505←404, 404←303, 303←202, and 202←101 involving the Ka=0 state and 523←422, 524←423, 422←321, 423←322, 321←220, 322←221 involving the Ka=2 state. These transitions showed structure due to fine, magnetic hyperfine and electric quadrupole interactions. The infrared spectrum, associated with the ν3 asymmetric vibrational mode of the NO2 monomer, consisted of three bands (RP0, RQ0, and RR0 and both K doublets of PP2, PQ2, and PR2) centered around 1615 cm-1. The data have been fitted to a semirigid Hamiltonian to determine the molecular parameters. The derived parameters are analyzed in terms of those of the free NO2 radical. Changes in these parameters upon complexation can be caused by a geometric effect due to the rotation of the inertial axes from the monomer to the complex, and an electronic effect caused by a distortion of the electronic wave functions on complex formation. The electronic changes (which may give an indication of incipient chemical bond formation) are shown to be very small. The absence of odd Ka″ states in both the infrared and microwave spectra was rationalized in terms of a high frequency tunneling motion of the NO2 within the complex. Both a dynamics calculation and a model potential based on atom–atom interactions provided additional support for a nonplanar equilibrium structure with a low barrier to planarity. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The infrared spectrum of the rare gas–spherical top complex Ne–SiH4 has been recorded in a supersonic jet in the region of the SiH4 ν3 triply degenerate stretching vibration at ∼2189 cm-1. In contrast to the previously measured Ar–SiH4 spectrum which showed almost equal rotational spacings within each band (corresponding to transitions between different internal rotor states of SiH4 within the complex), the Ne–SiH4 spectrum is complex with no obvious regular band structure. However, by analogy with the Ar–SiH4 spectrum, four bands of the Ne–SiH4 have been assigned and analyzed in terms of Hamiltonians incorporating Coriolis interaction between the angular momentum of the SiH4 monomer unit and the overall end over end rotation of the complex. These bands correlate with the SiH4 R(0) (K=0←0, K=1←0) and P(1) (K=0←0, K=0←1) transitions. Derived rotational constants demonstrate that the neon–silane separation (∼4.13 Å in the ground vibrational state) is larger than expected by analogy with Ar–SiH4, indicative of nearly free internal rotation by the silane monomer unit in Ne–SiH4. The smaller anisotropy of Ne–SiH4 compared with Ar–SiH4 results in a new angular momentum coupling scheme. Transitions arising from 22Ne–SiH4 correlating to SiH4 R(0) have also been observed and fitted; the higher than anticipated intensities demonstrate a novel isotope enrichment effect in the supersonic jet which is discussed. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A model for the rovibrational energy levels of a complex formed between a rare gas atom and a spherical top molecule is developed, specifically for a tetrahedral XY4 molecule in its ground and its triply degenerate vibrational states. Under the assumption that the tetrahedral molecule remains undistorted upon complexation, a large amount of the tetrahedral symmetry is retained in the complex. Using symmetry adapted terms to represent the anisotropy of the intermolecular potential, the perturbations to the energy levels of the tetrahedral molecule caused by the intermolecular potential have been considered. Correlation diagrams showing the pattern of these internal rotor states between the free rotor and rigid molecule limits have been constructed. [ABSTRACT FROM AUTHOR]

The infrared spectrum of Ar–SiH4, a rare gas–spherical top van der Waals complex, has been recorded in the vicinity of the silane ν3 triply degenerate stretching vibration ∼2189 cm-1. A complex, dense spectrum is observed, and this is due to the observation of 12 bands with origins corresponding to transitions between different internal rotor states of the silane molecule within the complex. From the analysis of the rotational structure within each band, the average argon–silane separation is determined to be 4.043 Å in the ground vibrational state and 4.046 Å in the excited vibrational state with v3=1. Using a model developed previously and a very simple form for the intermolecular potential, these 12 bands have been assigned and an effective anisotropic intermolecular potential for the internal rotation of the silane molecule within the complex has been determined. The vibrational anisotropy responsible for lifting the threefold degeneracy of the ν3 vibration is found to be fairly small, of the order of 1 cm-1, while the rotational anisotropy is much larger, of the order of 90 cm-1. [ABSTRACT FROM AUTHOR]

Pays tribute to British physicist Richard Graham. Factual background on his education and career as a scientist and educator; Contribution to the field of computational chemistry; Awards garnered throughout his career.

Pulsed molecular beam spectra of the CH[sub 4]-OCS complex have been recorded using both a molecular beam infrared diode laser and a Fourier transform microwave spectrometer. Analysis of the spectrum yields a near T shape structure with a centre of mass separation of 3.83å and a CH[sub 4] centre of mass-OCS centre of mass-oxygen angle of 73°. Splittings attributed to the internal rotations of methane within the complex have been observed in the microwave spectrum. The rotational constants of the complex for the A and T librational states of CH[sub 4] were determined. The differences (T- A) in the rotational constants were ΔA = 0.35, ΔB =-1.60 and ΔC =-1.85 kHz. [ABSTRACT FROM AUTHOR]

Anisotropic potential energy surfaces for Ne HCl, Kr HCl and Xe HCl are obtained by simultaneous least squares fitting to molecular beam spectra and rotational line broadening cross sections. A revised potential surface for Ar HCl is also presented. The potentials are all very similar in shape, with the absolute minimum at the linear rare gas–HCl geometry in each case. The absolute well depths and well depth anisotropies increase steadily as the size of the rare gas atom increases. wall of the potential. The molecular beam spectra for Ne HCl can be fitted only by a potential with a significant secondary minimum at the linear Ne Cl–H geometry, but the existing data for the more anisotropic Ar, Kr and Xe systems are not sensitive to the presence of this potential feature. The potential surfaces for these systems have accordingly been constrained to have a similar secondary minimum near the linear rare gas–ClH geometry. Experiments which would provide further information on the intermolecular potentials are suggested and predictions of the results are made. The potentials should be reliable in the region of the absolute minimum and on the repulsive. [ABSTRACT FROM AUTHOR]

We investigated the differential responding of 100 male inmates to subtle and obvious MCMI scale items; subtlety was determined by judgments by college students. It has been predicted that item subtlety would be positively correlated with item endorsement. This prediction was supported across all 175 MCMI items. as well as across items on 7 of 8 personality and 8 of 12 clinical scales. It had also been predicted that education and intelligence would moderate the relationship between subtlety and endorsement, with inmates higher in education and intelligence demonstrating a greater tendency than other inmates to avoid obvious items. Modest support was obtained for this prediction, with statistically significant results found for 4 personality and 5 clinical scales. The significance of the subtle-obvious distinction is discussed, especially when employing the MCMI with an inmate population. [ABSTRACT FROM AUTHOR]

The rotationally resolved spectrum of the dimer (NO monomer N O upsilon vibrational band using a diode laser absorption spectrometer which 2 3 incorporates a multiple-pass cell and a pulsed-jet expansion. A double-modulation technique involving a fast modulation of the laser frequency and a slow modulation of the gas pulse has been developed in the experiments. The spectrum is completely analysed and the rotational constants and effective structures are accurately determined for both the ground and the excited vibrational states. The centrosymmetric slipped parallel structure of (N O explained by an intermolecular potential containing a combination of electrostatic interactions between distributed multipoles of different monomers and atom-atom Lennard-Jones potentials to describe the repulsion and dispersion interactions. ) has been recorded in the region of the is well. [ABSTRACT FROM AUTHOR]

The microwave spectrum of OCS trimer, measured between 6 GHz and 18 GHz using Fourier-transform microwave spectroscopy, is consistent with a very asymmetric rotor, kappa = 0.18. A - and c-type transitions are observed with many lines showing a fine doubling of less than 20 kHz. A fit of average line positions to Watson A reduction (IR) rotational parameters gives; A = 847.97958(2), B = 736.17579(2), C = 574.32591(1) MHz, Delta J = 0.45440(9), Delta JK = 0 1572(5), Delta K = 0.3010(5), delta J = 0.06797(4), delta K = 0.0339(3)kHz. From a sum of electrostatic and Lennard-Jones pair interaction potentials, the model trimer equilibrium structures are chiral, suggesting the observed splitting is the result of tunnelling interconversion between enantiomers. A scheme employing the recursion relation for associated Legendre polynomials is used to extend the distributed multipole method for the electrostatic interaction between linear molecules to include multipole moments up to the highest order available from ab initio calculations. [ABSTRACT FROM AUTHOR]

Comments on the methods and applications of distributed multipole analysis to determine the charge distribution of molecules. Effects of molecular interaction; Calculation of wavefunctions in terms of gaussian functions and electron density; Convergence of multipole expansion.