Nuclear quadrupole hyperfine structure in 2_{1,2} ← 3_{0,3} and 1_{1,1} ← 2_{0,2} rotational transitions of CH_{2}^{35}Cl_{2} at 9.2 and 15.9 GHz, respectively, was measured with a newly constructed pulsed supersonic beam, cavity Fourier transform microwave spectrometer. All components of nuclear quadrupole splitting tensors of the chlorine nuclei in inertial and in principal quadrupole axes were determined. It is shown that in methylene halide molecules nuclear quadrupole information leads to a value for ∠(XCX) which is systematically larger than ∠(XCX) defined by the positions of the nuclei. Some novel features of the spectrometer are also described.
[Fe₃(hyetrz)₆(H₂O)₆](CF₃SO₃)₆ (where hyetrz = 4-(2'-hydroxyethyl)-1,2,4-triazole) is an interesting linear, trinuclear iron(II) compound with incomplete spin crossover. We reinvestigated crystal structure of this compound in the wide temperature range because the knowledge only about the crystal structure in the initial and final phases is not sufficient to establish correlations between the structural and magnetic properties of the spin crossover system. The complex [Zn₃(hyetrz)₆(H₂O)₆](CF₃SO₃)₆ was used for comparison because it does not exhibit spin crossover phenomenon and it is isostructural with a high spin phase of Fe(II).
Stability of motions for different potential functions describing vibrational motions of rotating molecule has been discussed. It was shown that an equilibrium position for nonrotating r_{0} and rotating r_{J} molecules for almost all the examined potentials is a node, but for the molecule described by the soft body model a critical value of rotation quantum number J_{c} occurs above which r_{0} is a saddle point, and the stable motion may occur only around r_{J}.
Highly-resolved photoabsorption spectra of SiX_{4} molecules (with X = H, D, F, Cl, Br), recorded by photoionization in the region of the Si-2p absorption thresholds, are presented. Vibrational fine structure could be resolved in all cases, allowing a derivation of vibrational energies and intra-molecular distances of the core-excited molecules from Franck-Condon fits. In case of the heavier ligand atoms, spectral features arising from thermally-excited vibrational states of the electronic ground state were observed. The results obtained for the various ligand atoms are compared with each other and are discussed in the context of the equivalent-cores approximation.
The rotational spectrum of the two most abundant isotopomers of the weakly bound dimer between dinitrogen and hydrogen bromide, ^{14}N_2···H^{79}Br and ^{14}N_2···H^{81}Br, has been measured for the first time. The three lowest J transitions, at frequencies from 2 to 8 GHz, have been studied at conditions of supersonic expansion. The complicated hyperfine splitting structure arising from the three non-equivalent quadrupolar nuclei has been assigned and fitted. The resulting spectroscopic constants and the derived molecular quantities are compared with those for other isotopomers, as well as with experimental and calculated results for other linear dimers involving dinitrogen. A revised value for the nuclear quadrupole splitting constant for free nitrogen molecule,ρ(N)=-5.3(1) MHz, is also derived.
Lithium amide (LiNH_{2}) and imide (Li_{2}NH) have recently attracted much attention as part of the Li-H-N system suitable for hydrogen (H) storage applications. However, the ground-state imide structure is still unknown with at least six candidate structures, with ground state energies all very close to one another. In order to discover possible pathways for the imide-amide-imide transformations during the hydrogen absorption/desorption cycles, we have examined the molecular structures involved (along with their changes during these processes) using ab-initio calculations based on the linear combination of atomic orbitals (LCAO). In addition, the influence of Li substitution by some other elements of interest on the system behaviour was investigated. These analyses were complemented by density functional theory (DFT) calculations of several crystal structures appearing in the processes. In this way a thorough insight into the structures and the processes taking place at atomic level is attained, providing a starting point for understanding these complicated systems, and the mechanisms governing their transformations.
The weakly bound van der Waals dimer between a molecule of cyanoacetylene and an argon atom was observed by rotational spectroscopy of supersonic expansion. Cyanoacetylene was generated in situ from vinyl cyanide precursor by means of a high voltage discharge just downstream of the expansion nozzle. Both ^bR- and ^bQ-type rotational transitions were measured and rotational, centrifugal distortion, and nuclear quadrupole splitting constants were determined. Analysis of the data shows that ground state geometry of the dimer is characterised by R_{cm}=3.65Å andθ=94.9º, with the Ar atom shifted from the position above the cyanoacetylene centre of mass in the direction of the CN group.
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