Journal of Molecular Spectroscopy最新文献

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling in the H₃C⁻ anion and H₃Si radical is analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. We used the following two vibrational coordinates for the H₃X structure (X = C, Si): the distance of the X atom from the plane of a regular triangle formed by three hydrogen atoms (1) and a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms (2). The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H₃C⁻ at the CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, CCSD(T)/aug-cc-pV5Z, CCSD(T)/CBS(TQ5), CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/t-aug-cc-pVTZ, and CCSD(T)/q-aug-cc-pVTZ levels of theory, based on recommendations from recently published work [M.C. Bowman, B. Zhang, W.J. Morgan, H.F. Schaefer III, Mol.Phys., 117 (2019) 1069–1077]. The same 2D PES for the H₃Si radical was calculated at the CCSD(T)/aug-cc-pVDZ CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, and CCSD(T)/CBS(D,T,Q) as well as at the CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVQZ levels of theory. The tunneling splittings for the D₃C⁻ anion and D₃Si radical were calculated as well. The results of calculations demonstrate good agreement with available experimental data on umbrella vibration frequencies and inversion splittings for the title molecules.

The polarisation labelling spectroscopy technique was applied to study the C${}^1{\Pi }_u$ $\leftarrow$ X${}^1{\Sigma }_g^{+}$ band system in potassium dimer. About 1100 new rotationally resolved molecular lines were measured in the 22100–24100 cm⁻¹ spectral range. Perturbations of the lowest vibrational levels of the C state were localised and their origin discussed. A set of Dunham coefficients was deduced to fit the unperturbed levels of the C${}^1{\Pi }_u$ state with $0\le v\le 38$ and $18\le J\le 101$ and the potential energy curve of the state was constructed.

We report spectroscopic observation and theoretical calculations of a new isomer of (CS₂)₃ as observed in the regions of the ν₃ fundamental band of CS₂ (6.5 μm) and the ν₁ + ν₃ combination band (4.5 μm), using tunable laser sources and a pulsed supersonic slit-jet. The previously observed CS₂ trimer has a barrel-shaped structure with three equivalent monomers and D₃ symmetry. The new isomer consists of a staggered parallel “dimer pair” of equivalent CS₂ monomers with a third CS₂ monomer sitting “on top”, similar to the known non-cyclic CO₂ trimer. This structure has C₂ rotational symmetry corresponding to the b inertial axis of the trimer, as proven by observed nuclear spin statistics. Ab initio calculations correctly give the two observed isomer structures and indicate that they lie very close in binding energy.

Neutral and ionic N₂ species exhibit a rich spectrum as a result of the large density of couplings between states with different multiplicities. In this sense, spectra of the molecular ion N${}_2^{+}$ are investigated combining Fourier transform spectroscopy and ab initio methods. We have reanalyzed the First Negative band System (B${}^2{\Sigma }_u^{+}$ $\to$ X${}^2{\Sigma }_g^{+}$) including five bands not reported previously by Fourier spectroscopy. The spectra were recorded using a resolution of 0.6 cm⁻¹ and accuracy of 0.005 cm⁻¹. These results are then compared with new MRCI+Q/AV6Z calculations. For the first time, transition probabilities are computed for the previously observed 2${}^2{\Pi }_g$-A${}^2{\Pi }_u$ band system. The 2${}^2{\Pi }_g$ state ($T_e$ = 67,029 cm⁻¹) has a dissociation energy of 24,787 cm⁻¹ at $R_e$ = 2.7332 a₀. The predicted lifetimes for the 2${}^2{\Pi }_g$-A${}^2{\Pi }_u$ emissions are of the order of 170 ns. The calculated transition probabilities A($v^{\prime }$=0, $v^{\prime \prime }$=0) for the B${}^2{\Sigma }_u^{+}$-X${}^2{\Sigma }_g^{+}$ and 2