The microwave spectrum of vinylcyclopropane

Frequencies of rotational transitions in the microwave region are reported for the ground and three torsionally excited states of the species of vinylcyclopropane in which the vinyl group is trans to the cyclopropane ring and there is a plane of symmetry. Transitions in the species with ¹³C substitution at the out-of-plane carbon site are also reported. An extensive search for transitions belonging to another species was not successful. The torsional excitation energy is estimated from relative intensity measurements to be 125 cm^?1. The dipole moments determined from the Stark effect ar μ_a = 0.486 ± 0.007 D, μ_c = 0.110 ± 0.010 D and μ = 0.498 ± 0.007 D.     

The dipole moment of the FO radical

The electric dipole moment of the FO radical (${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$) has been directly measured by observing its saturated absorption laser magnetic resonance spectrum (v = 1 ← 0) in the presence of a moderate electric field. The resulting dipole moment [μ(v = 0) = 0.0043(4) D, μ(v = 1) = 0.0267(9) D] is extremely small, and shows a large relative change with vibrational state. The sign of the dipole moment is the same for the two vibrational states. Previous failures to detect microwave or gas phase EPR spectra of FO are fully explained by this small dipole moment.     

The rotation-torsion contour of the 2668 Å origin band of toluene. High-resolution 295 K absorption spectrum

The 2668 Å vibrational origin band of toluene was measured and analyzed using an asymmetric-top/free-internal-rotor model. The change in the methyl group geometry between the ground (^eA′₁) and the excited ^eA″₁ ($\text{ππ}{}^1$) state was found to be slight. Rough values found for the changes in the phenyl frame rotational constants are similar to those for other monosubstituted benzenes with substituents lacking lone-pair electrons. The torsional structure in the toluene origin band is blue-degraded whereas the rotational structure in each Δm = 0 torsional manifold of transitions is red-degraded. Deconvolution of the torsional structure in the calculated contour shows that strong R-branch heads for transitions emanating from each torsional level of the ground state persist in the experimental contour for 0 ≤ |m| ≤ 12.     

The rotation-torsion contour of the 2668 Å origin band of toluene. Calculation of the molecular beam fluorescence excitation spectrum

The rotation-torsion contour of the low-temperature molecular beam fluorescence excitation spectrum of toluene was analyzed within the framework of the asymmetric-top/free-internalrotor model. The features observed in the moderate-resolution spectrum are reproduced well by this calculation, suggesting that the zero barrier approximation in both the ground and excited states is acceptable even at the low temperatures achieved in the supersonic jet expansion. The values of the excited-state rotational constants are found to be the same as those obtained in the analysis of the high-resolution 295 K spectrum. Corroboration for sequence band assignments in the 295 K spectrum is also given.     

Vibration-rotation transitions in the CF radical, studied by laser magnetic resonance spectroscopy at 7.8 μm

Several transitions in the vibration-rotation spectrum of the CF radical in its X²Π state have been detected by CO-laser magnetic resonance. In addition to strong resonances for the ²Π_3/2-²Π_3/2 transitions in the fundamental band at 1286 cm⁻¹, weaker “cross” ²Π_3/2-²Π_1/2 and hot band transitions have also been observed. The ¹⁹F nuclear hyperfine splitting is clearly resolved for almost every transition. These observations provide an interesting comparison with the recent study of the same (1, 0) band of CF by diode laser spectroscopy.     

Ion-enhanced gas-surface chemistry: The influence of the mass of the incident ion

There are many examples of situations in which a gas-surface reaction rate is increased when the surface is simultaneously subjected to energetic particle bombardment. There are several possible mechanisms which could be involved in this radiation-enhanced gas-surface chemistry. In this study, the reaction rate of silicon, as determined from the etch yield, is measured during irradiation of the Si surface with 1 keV He⁺, Ne⁺, and Ar⁺ ions while the surface is simultaneously subjected to fluxes of XeF₂ or Cl₂ molecules. Etch yields as high as 25 Si atoms/ion are observed for XeF₂ and Ar⁺ on Si. A discussion is presented of the extent to which these results clarify the mechanisms responsible for ion-enhanced gas-surface chemistry.     

Emission spectra of polyatomic radical cations in the gas phase: Ã2Πu → X̃2Πg band systems of Cl(CC)2 Cl+, Br(

Emission spectra of the dihalodiacetylene radical cations, X(CC)₂X⁺ with X = Cl, Br and I, excited in the gaseous phase by low energy e     

The electronic structures of some aromatic sulfinylamines

He(I) and He(II) photoelectron spectra of some sulfinylamines are reported and assignments made on the basis of CNDO/S LCAO MO calculations. Insight into the effects of several substituents on the electronic structures of the compounds is obtained. The difference between the actual electronic structure of o,o′, p-trimethyl sulfinylaniline and that interpolated from other molecules in the series is assumed to reflect a different conformation for this compound.The results of the MO calculations agree fairly well with the experimental data, although some discrepancies occur, concerning especially the π-donating capacity of a Cl substituent, and ionizations from chlorine lone pair orbitals.     

The reaction of nitrous oxide with rhodium

A clean rhodium filament at room temperature is highly reactive towards nitrous oxide. The oxygen atom of the N₂O molecule is adsorbed with a sticking probability of 0.45 whilst the nitrogen atoms appear in the gas phase as molecular nitrogen. The room temperature uptake of oxygen is about 5 × 10¹⁴ atom cm^?2 and is independent of nitrous oxide pressure in the range 3.5 × 10^?8 to 1.1 × 10^?6 torr. The adsorption curve is of typical form with an initial region of essentially constant sticking probability. For the first 80% of adsorption at room temperature the shape is satisfactorily accounted for if molecules are able to visit 4–5 adsorption sites whilst held in a weakly-bonded precursor state.     

The interaction of hydrogen with stepped surfaces of copper: A pairwise-additive model

A pairwise-additive model, with Morse functions as the two-body potentials, has been employed to study stepped surfaces of copper. In general, the hydrogen-atom-copper bond energy is increased when one or more copper atoms are added to the surface at sites different from that which the hydrogen atom is approaching. Approaches of the hydrogen atom to a step face produced hydrogen-copper binding energies larger than those found in the absence of the step. Variations in these general observations are noted for alterations of the approach site environment.     

The autocatalytic decomposition of acetic acid on Ni(110)

The flash decomposition of CH₃COOH was studied on a clean nickel (110) surface following adsorption at 30° C in order to access the applicability of chemical reaction rate theory to a homologous series of reactants on a well-defined surface. As was observed for formic acid, acetic acid adsorbed at 30° C to yield gaseous H₂O and to form islands of adsorbed anhydride intermediates; the decomposition proceeded by a two-dimensional auto-catalytic mechanism to form H₂, CO₂, Co and surface carbon. The decomposition of the anhydride was rate determining for the formation of CO₂ and H₂. The rate of decomposition was well described by the equation governing the formic acid decomposition on the same surface. The activation energy for this first order decomposition was determined to be 28.2 $\text{kcal}\text{gmol}$ and the pre-exponential factor, v, was found to be 6.4 × 10¹⁴ s^?1 with a fraction of initiation sites of 0.004. These values were nearly the same as those observed for the decomposition of HCOOH, suggesting identical intramolecular mechanisms for the unimolecular decomposition of the adsorbed intermediates. The relative values of v for the decomposition of HCOOH, DCOOH and CH₃COOH indicated that the motion of the H, D or CH₃ group was involved in the rate-limiting step.     

A theoretical study of the substituent effect on the infrared intensities of the CN stretching mode of benzonitrile derivatives

The substituent effect on the integrated intensities of the characteristic CN infrared band of benzonitrile derivatives was studied using the CNDO/2 method. The charge flux term plays an important role in the substituent effect on the intensities and the fixed charge term does not have a predominant effect on the intensities. The contributions of the π, , and σ electron systems to the charge flux term are discussed in detail.     

The crystallographic shear planes of the non-stoichiometric molybdenum oxides as revealed by RHEED: Investigation from the Mo18O52(100) surface

Large Mo₁₈O₅₂ crystals are obtained by an appropriate crystallization method. The examination of their well developed surfaces by the use of reflection high energy electron diffraction (RHEED) proves that these are (100) surfaces stepped along [010] directions. It is concluded that this oxide surface conformation can be connected to the particular Mo₁₈O₅₂ structure which is built up of MoO₃ slabs of finite width mutually joined by crystallographic shear planes (CS planes). Transmission electron microscopy (TEM) analysis from Mo₁₈O₅₂ crystal flakes confirms that these are single crystals without disorder in the periodicity of the CS planes.     

The adsorption and condensation of oxygen on aluminium at low temperaturf

The interaction of oxygen with an Al(111) surface at 30 K leads initially to dissociative adsorption, followed by the physisorption of molecular oxygen. The latter is characterised by HeI and HeII UPS spectra similar to the gas phase. The physisorbed molecules partly convert into the dissociated phase on standing in vacuum. There appears to be no difference between the UPS spectrum of a condensed layer of oxygen and that of the physisorbed species.     

The identification of two entrance channels in the reaction of metastable helium He(23S,21S) with SO2

The energy spectrum of electrons emitted in the reaction of He(2³S) and He(2¹S) with SO₂ indicates that in addition to the covalent entrance channel a strongly attractive ionic channel plays a role. We find upper limits for the well depth of the potential curve that corresponds to the latter channel of D_e ? 3.5 eV and D_e ? 4.3 eV for He(2³S) and He(2¹S) as the reaction partner, respectively. The partitioning between the two entrance channels can be understood by assuming the coupling matrix between both channels to depend strongly on the orientation of the SO₂ molecule with respect to the incident metastable He*.     

Physical adsorption on heterogeneous surfaces: The effect of the topography of surfaces on the evaluated adsorption energy distribution

It has been known for a long time that the topography of surfaces is a very important factor governing the adsorption on heterogeneous solid surfaces. In spite of this, all methods to evaluate the adsorption energy distribution, developed so far were based on the patchwise model of heterogeneous surfaces. The purpose of this paper is to show how the well-known Condensation Approximation method can be applied to determine the adsorption energy distribution on the heterogeneous surfaces with a fully random topographical distribution of sites. The method is developed for the case of localized adsorption with nearest-neighbour interaction between admolecules.     

Influence of Doppler broadening on the stability of monomode ring lasers

We consider a single running mode in a ring gas laser where inhomogenous Doppler broadening is dominant. The analytic linear stability analysis of the stationary solution leads to the conclusion that in the bad cavity limit a second threshold exists; a salient property is that it occurs at low intensity in contradistinction to homogeneously broadened media where it occurs at high intensity.