Millimeter-wave spectrum of Ne–CO: new measurements

The b-type rotational transitions of the van der Waals complex, Ne–CO have been measured using the intracavity OROTRON jet spectrometer in the frequency range of 80–115 GHz. The high sensitivity of this technique enabled us to detect all three Ne isotopic modifications of the complex, ²⁰Ne–CO, ²²Ne–CO, and ²¹Ne–CO in natural abundance. The observed and assigned transitions belong to the Q-branch of the K = 1–0 subband and include also R (0) and P (2) lines. The newly obtained data were analysed together with previously observed millimeter-wave b-type and microwave a-type rotational transitions.     

Assignment and Power Series Analysis of the FIR Fourier Transform Spectrum of Cyanamide Using a Multimolecule Ritz Program

The “Ritz” program, originally written for the analysis of the Fourier transform spectra of the methanol isotopomers and presented in previous papers, has been extended in order to analyze the spectra of other molecules. This program evaluates the term values involved in the assigned transitions by the Rydberg–Ritz combination principle, and can tackle such perturbations as Fermi-type resonances or Coriolis interactions. As a first application of the extended version, we present an investigation of the Fourier transform spectrum of cyanamide between 25 and 980 cm⁻¹. More than 16 000 lines have been assigned. Our Ritz database now comprises a list of more than 19 000 assigned lines (including of the microwave and FIR lines available in the JPL database) and more than 3900 term values. All of the lines presented in this paper correspond to transitions within the ground and first excited inversion levels of the ground vibrational state of the small-amplitude modes.     

Higher energy states in the CO dimer: millimeter-wave spectra and rovibrational calculations

New extensive millimeter-wave measurements of the 12C16O dimer have been made, and more than 300 new spectral transitions have been observed in the frequency range 81-135 GHz. A joint analysis of these and previous millimeter-wave data yielded the precise location of 33 new energy levels of A+ symmetry and 20 levels of A- symmetry. These energy levels are located at 8-18 cm(-1) above the zero-point level. Some of them belong to already known stacks, and others make up 9 new stacks of the dimer. Newly determined stacks have K=0, 1, and, for the first time, 2, where K is the projection of the total angular momentum on the intermolecular axis. The energy levels from accompanying rovibrational calculations with the use of a recently developed hybrid CCSD(T)/DFT-SAPT potential are in very good agreement with experiment. Analysis of the calculated wave functions revealed that two new stacks of A+ symmetry with K=2 correspond to overall rotation of the dimer while the other newly observed stacks belong to the geared bend overtone modes. The ground vibrational states of the two "isomers" found are more or less localized at the two minima in the potential surface, whereas all the geared bend excited states show a considerable amount of delocalization.     

Transmission of Molecular Structure on NMR Characteristics of Phosphorus-Nitrogen Double Bond Systems

Abstract

Elucidation of the origin for the large variability of 31P and I5N chemical shifts in compounds with P-N double bonds is a challenging task. We demonstrate here how trends in 3lP and 15N chemical shifts of iminophosphines and ylene-iminophosphoranes can be explained by the use of quantum chemical model concepts.     

Quadrupolar [14](meta-ortho)2azolophanes. Intramolecular C-H…N and to Water C-H…O hydrogen bonding revealed by X-ray diffraction

The first X-ray crystallographic diffraction of an example of the title heterophanes built up from heterocyclic betaine subunits is reported and its quadrupolar character is confirmed. The crystal packing of 2·4H₂O is mainly governed by hydrogen-bonding networks, strong intermolecular interactions with water together with weak interactions, either intramolecular or with water.     

The QKa, Branches of Carbodiimide, HNCNH, between 1.8 and 3.3 THz

The ^rQ_Ka branches of carbodiimide, HNCNH, have been recorded with a tunable far-infrared spectrometer. The ^rQ_Ka branches with K_a { 2, 3, 4 }, which occur at approximately 1.8, 2.5, and 3.2 THz, respectively, were measured rotationally resolved. The torsional doublet splitting observed in the ^rQ₀ branch and several ^rR branches by Birk et al. (J. Mol. Spectrosc.136, 402-445 (1989)) was also observed in all the Q branches reported here. In addition, anomalous K_a-type doubling was detected within the ^rQ₂ branch for rotational quantum numbers J > 18. Molecular constants were obtained by fitting the line positions, including older data, with Watson′s Hamiltonian in S-reduction. The anomalous K_a-type doubling could be described as a centrifugal distortion interaction with ΔK_a = 4. The splitting is called anomalous because it inverts the K_a = 2 energy levels of an accidentally nearly prolate symmetric top molecule (Ray′s asymmetry parameter for HNCNH κ = −0.999995343(32)).     

On the waves and instability in self-gravitating magnetic molecular clouds with ambipolar diffusion Part 2: Cylindrical modal approach and nonlinear effects

The dynamics and evolution of molecular clouds, which are the main sites of active star formation in our Galaxy, are governed by the interaction of the self-gravity, magnetic fields, and ambipolar diffusion, in the form of waves and instability. In our earlier paper (Part 1), we carried out a detailed planar modal analysis. The present paper (Part 2) is an extension of Part 1 in order to include the three-dimensionality and the finite size of the cloud as well as the nonlinear effects. A cylindrical modal approach is developed to take into account the three-dimensionality and the finite size of the cloud as well as the special direction of the mean field B ₀. Dispersion relation and solutions of such cylindrical modes are obtained. It is shown that, in the most unstable direction (∥ B ₀), the growth rate is considerably reduced by the finite lateral size compared with the planar mode of the same wavelength. Nonlinear effects of the magnetic field and magnetic waves are discussed, with particular attention paid to their dependence on the coupling factor σ which is the ratio between the mean collision frequency of a neutral with ions and the gravitational response frequency. It is shown that fast magnetosonic waves are as important as Alfvén waves in the global support of the cloud. In order that the lower limit of the wavelengths in the moderately dissipative range of such waves is small compared with the cloud size, σ should be larger than 5. It is also shown that σ should be larger than 7.3 in order for the density growth of the neutral fluid in a free-fall time to be smaller than 30%. A typical value of σ ≈ 11 in molecular clouds is estimated. This corresponds to an ionization rate ζ = 10^?17 and a metal depletion δ = 0.1. For the clouds with such value of σ, both the density growth and the flux loss are smaller than 20% in a free-fall time. It is shown that a self-adjusting mechanism is able to slow down the global collapse at the early stage of cloud evolution in terms of the interaction between the global collapse and the then existing Alfvén and fast magnetosonic waves, which originate from the inhomogeneous velocity and density distributions in the cloud. Such interaction will not only strengthen these waves, but also create outwards decaying amplitudes of the field perturbation and therefore generate outward net magnetic forces to support the cloud against global collapse. The same mechanism also works for refreshing the outwards propagating Alfvén and fast magnetosonic waves caused by star-forming or core-forming activities, if the total energy supply rate due to these activities is lower than the total dissipation rate of these waves. In this way, a significant portion of the released gravitational energy during the global collapse is tapped and turned into the magnetic waves to slow down the global collapse itself. In terms of such a mechanism, the property that the dissipation rate of Alfvén and fast magnetosonic waves increases with the wave number leads to a simple explanation of the coexistence of the global quasi-stability and the local instability (formation of dense cores) in molecular clouds with cloud mass much larger than the Jeans mass.