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.     

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.     

Inversion of the Ka = 0 and 1 rotational levels in the lowest excited vibrational state of HNCS

Fairly strong, regularly spaced absorption lines have been observed in the microwave spectrum of HNCS and assigned to b-type, K_a = 0 ← 1, Q-branch transitions arising from molecules in the lowest excited vibrational state. The Fortrat diagram of these lines has the appearance of a c-type Q branch, which is impossible in HNCS because of its symmetry. This anomalous b-type Q-branch spectrum is caused by strong a-type Coriolis interactions among the three low-lying bending modes; the K_a = 1 levels of the lowest excited vibrational state are perturbed and shifted lower in energy than the K_a = 0 levels for each J. This interpretation has been confirmed by the observation of P- and R-branch transitions associated with this Q branch. The band origin has been determined to be ?40 104.287 MHz (?1.3377 cm^?1). The inversion of the K_a = 0 and 1 energy levels is consistent with the interpretation of HNCS as a quasi-linear molecule.     

The infrared spectrum of fulminic acid,HCNO, in the ν4 fundamental region

The infrared spectrum of fulminic acid, HCNO, was measured with high resolution in the region 500–657 cm^?1. The spectrum was obtained with a Bomem interferometer, at a reslution of about 0.006 cm^?1. Thirteen bands could be identified and assigned to rovibrational transitions of HCNO. These are the fundamental ν₄ and some of its hot bands, and the overtone 2ν₅ and some of its hot bands. Because ν₅ is a quasilinear bending mode, the identification and measurement of the various hot bands is especially important for locating the combination states of ν₄ with various quanta of ν₅.     

The pure inversion spectrum of 15ND3 in the v2 = 1 state

The inversion spectrum of ¹⁵ND₃ in the v₂ = 1 state was investigated in the millimeter wave region between 70 and 125 GHz. The inversion splitting (J = 0, K = 0) was calculated to be 97 279.998(35) MHz. The K = 3 splitting constants and the electric dipole moment have also been determined.     

High-resolution infrared spectrum and rovibrational analysis of the ν3 fundamental of diazirine,H213CN2

The high-resolution infrared spectrum of ¹³C-diazirine was recorded using a high-information Fourier transform spectrometer with a resolution of 0.0054 cm^?1. The rovibrational structure of the ν₃ fundamental at 1458.1884 cm^?1, which is an A-type parallel band (¹³CH₂ deformation) was assigned and analyzed with extensive use of modern methods of spectrum simulation. The rovibrational assignment and the molecular constants determined for the excited vibrational level of this band are given.