On the construction of quasidiabatic state representations of bound adiabatic state potential energy surfaces coupled by accidental conical intersections: incorporation of higher order terms

The quadratic vibronic coupling model is an important computational tool for simulating photoelectron spectra involving strongly coupled electronic states in polyatomic molecules. However, recent work has indicated the need for higher order terms, with most of the initial studies focusing on molecules with symmetry-required degeneracies. In this study we report an extension of our approach for constructing fully quadratic representations of bound electronic states coupled by conical intersections, which allows for the inclusion of higher order terms, demonstrated here employing a quartic expansion. Procedures are developed that eliminate unphysical behavior for large displacements, a problem likely to be an endemic to anharmonic expansions. Following work on representing dissociative electronic states, Lagrange multipliers are used to constrain the constructed representation to reproduce exactly the energy, energy gradients, and∕or derivative couplings at specific points, or nodes, in nuclear coordinate space. The approach is illustrated and systematically studied using the four lowest electronic states of triazolyl, (CH)(2)N(3).     

A dynamic disorder‐linked reversible phase transition in a new chloroform solvate of cis‐dichloridobis(triethylphosphane)platinum(II)

The title compound, cis‐dichloridobis(triethylphosphane)platinum(II) chloroform monosolvate, [PtCl₂(C₆H₁₅P)₂]·CHCl₃, has been obtained from ligand scrambling in the cis‐[PtCl₂(Cyp₂PCl)(PEt₃)] (Cyp = cyclopentyl) system in CHCl₃ solvent. Unlike the two previously reported unsolvated polymorphs, which are both monoclinic, the compound crystallizes in an orthorhombic setting. Furthermore, the system exhibits a reversible temperature‐dependent structural phase transition, coupling a reduction in anisotropic displacement parameters and a reduction in crystallographic symmetry on cooling. The high‐temperature phase adopts space group Pnma with the complex and solvent molecules sitting across a crystallographic mirror plane (Z′ = 0.5). The low‐temperature phase adopts the space group P2₁2₁2₁ with Z′ = 1.     

On the spin-isospin response at intermediate energies

We have calculated the response function of infinite nuclear matter to a spin-isospin probe in the transverse and longitudinal channels. The two channels are distinguished by the meson exchanged (ρ or π, respectively) in the ph and Δh interactions, in addition to the effective g′ interaction. In the intermediate-energy region the response is particularly sensitive to the Δ-dynamics in the nuclear medium. We have applied the results of a previous calculation, which is based on a self-consistent treatment of π- and Δ-propagation in nuclear matter, to obtain Δ-self-energy corrections in the medium. Due to the opening of many-body decay channels, the self-consistent mechanism supplies a strong quenching and spreading effect on the Δ-peak in the transverse channel and we find a remarkable contribution to the response function in the energy region corresponding to the dip in inelastic electron scattering. A comparison with the experimental data for the ¹²C(e, e') cross section is given. In the longitudinal channel, on the other hand, the coherent propagation of the intermediate pion has the effect of splitting the Δ-peak into two parts, due to the vanishing of the polarization propagator at the energy corresponding to the on-mass-shell pion. The self-consistent calculation again yields a quenching effect on the response which is particularly strong on the lower peak and pushes up the other one to higher energies.     

The effects of multichannel compression/expansion amplification on the intelligibility of nonsense syllables in noise

The effects of six-channel compression and expansion amplification on the intelligibility of nonsense syllables embedded in speech spectrum noise were examined for four hearing-impaired subjects. For one condition (linear) the stimulus was given six-channel amplification with frequency shaping to suit the subject's hearing loss. The other condition (nonlinear) was the same except that low level inputs, to any given channel, received expansion amplification and high level inputs received compression. For each condition, each subject received the nonsense syllables at three different input levels, representing low, average, and high intensity speech. The results of this study, like those of most other studies of multichannel compression, are mainly negative. Nonlinear processing (mainly expansion) of low intensity speech resulted in a significant degradation of speech intelligibility for two subjects and in no improvement for the others. One subject showed a significant improvement in intelligibility for the nonlinearly processed average intensity speech and another subject showed significant improvement for the high intensity input (mainly compression). Clearly, nonlinear processing is beneficial for some subjects, under some listening conditions, but further research is needed to identify the relevent characteristics of such subjects. An acoustic analysis of selected items revealed that the failure of expansion to improve intelligibility was primarily due to the very low intensity consonants /e/ and /k/, in final position, being presented at an even lower intensity in the expansion condition than in the linear condition. Expansion may be worth further investigation with different parameters. Several other problems caused by the multichannel processing were also revealed. These included alteration of spectral shapes and band interaction effects. Ways of overcoming these problems, and of capitalizing on the likely advantages of multichannel amplification, are currently being investigated.     

The reactions of some organotin(IV) chlorides with antimony(V) chloride and boron(III) chloride

The reactions of the organotin chlorides R_nSnCl_4?n(R = Me or Ph; ? n ? 4) with the Lewis acids SbCl₅ and BCl₃ have been investigated by ¹¹⁹Sn and (where appropriate) ¹¹B NMR spectroscopy. The results show that transfer of organo-groups to antimony or boron usually takes place rather than chloride abstraction to give cationic tin(IV) species, and this process is more facile for phenyl than methyl groups. These conclusions have been confirmed in some instances by isolation of the non-volatile reaction products.     

Magnetooptics

The field of magnetooptics since 1975 encompasses a vast amount of fundamental and applied work. This review deals briefly with a few particularly interesting developments. Under the topic of new effects are a magnetic linear birefringence linear in H and a birefringence arising from the gradient in M. Research applications include the visualization of antiferromagnetic domains and the current search for evidence of anyons in high temperature superconductors. Several examples are given of recent applied work on both bulk and film waveguide magnetooptical isolators as well as the materials used in them.     

Galvanomagnetic effects in graphite—I: Low field data and the densities of free carriers

Measurements of the galvanomagnetic properties of highly-oriented pyrolytic graphite have been made in the field range 0.001–1.5 T at 298, 77.4 and 4.2 K, with selected measurements to higher fields and ～1.2K. Specimens of graphite were chosen with properties approximating those of purified natural crystals (single crystals) of graphite. Attention is drawn to differences in the properties of these materials. The data are analyzed with particular emphasis on the density of free carriers and its dependence on temperature, since earlier work had shown that experimental results were appreciably different from theoretical predictions.     

Dispersion studies of the 22 GHz water vapor line shape II. Instrumental correction

Anomalies in the resonance dispersion of the pressure-broadened water vapor line at υ₀ = 22.235 GHz, which were reported in Part I,⁽¹⁾ are resolved. The pressure-scanning differential-refraction spectrometer (microwave dispersometer) gives rise to a signal enhancement as the line center moves within the width of the dispersion discriminator which is a dual-mode transmission cavity. Resonance absorption prevents the frequency of peak transmitted power from coinciding with the resonance condition of zero phase, thus systematically distorting the molecular resonance dispersion. An expression, valid for |υ − υ₀| greater than the cavity half width, is derived which predicts apparent departure from Lorentzian behavior. The results reported in I as well as results for the 23.6 GHz rotational 3_1,2 → 3_2,1 line of C₂H₄O (ethylene oxide) show a Lorentzian molecular line shape. At pressures above 1 torr nonresonant polarization effects become detectable. Instrumental distortion, and Doppler-, wall-, and saturation-broadening effects at low pressures (<50 mtorr) are accounted for only qualitatively to determine the resolving power and to define v₀.     

Laser induced fluorescence studies of iodine oxide chemistry. Part II. The reactions of IO with CH3O2, CF3O2 and O3

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k for the reactions IO + CH(3)O(2)--> products (R1, 30-318 Torr N(2)), IO + CF(3)O(2)--> products (R2, 70-80 Torr N(2)), and IO + O(3)--> OIO + O(2) (R3a). Values of k(1) = (2 +/- 1) x 10(-12) cm(3) molecule(-1) s(-1), k(2) = (3.6 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1), and k(3a) <5 x 10(-16) cm(3) molecule(-1) s(-1) were obtained at T = 298 K. In the course of this work, the product yield of IO from the reaction of CH(3)O(2) with I was determined to be close to zero, whereas CH(3)OOI was formed efficiently at 70 Torr N(2). Similarly, no evidence was found for IO formation in the CF(3)O(2) + I reaction. An estimate of the rate coefficients k(CH(3)O(2) + I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) and k(CH(3)OOI + I) = 1.5 x 10(-10) cm(3) molecule(-1) s(-1) was also obtained. The results on k(1)-k(3) are compared to the limited number of previous investigations and the implications for the chemistry of the marine boundary layer are briefly discussed.