Journal of Molecular Spectroscopy最新文献

The high-resolution rotational spectrum of chlorosulfonic acid (ClSO₂OH) has been studied using both broadband and cavity-based Fourier transform microwave spectrometers over the frequency range of 5–18 GHz. a-, b-, and c-type transitions have been recorded for both the ³⁵Cl and ³⁷Cl isotopologues. The observation of c-type lines establishes that the molecule lacks a plane of symmetry and suggests that the OH group can undergo large amplitude motion between equivalent structures. Interconversion between these structures can be achieved via internal rotation through two inequivalent barriers occurring at Cl-S-O-H torsional angles of 0 or 180 degrees. As in previous work on triflic and methanesulfonic acids, two states are observed and are treated as tunneling states which are presumed to arise primarily due to motion through the lower of the two barriers. The a- and c-type transitions occur within each of these states while the b-type transitions cross between them. Rotational, centrifugal distortion, and chlorine nuclear quadrupole coupling constants, as well as the energy difference between the two tunneling states and associated coupling constants, have been determined. The experimental tunneling energies, ΔE, for the ³⁵Cl and ³⁷Cl isotopologues are 52.6926(16) MHz and 52.6397(46) MHz, respectively. Quantum chemical calculations were carried out using MP2 and B3LYP density functional theory (DFT) methods with an aug-cc-pVTZ basis set. The rotational constants from the optimized structures were in good agreement with the experimental values. The lowest energy barrier for OH motion was calculated to be 2.63 kcal/mol at the B3LYP/aug-cc-pVTZ level. The effects of the large amplitude motion are similar to those recently reported for triflic acid (CF₃SO₂OH) and methanesulfonic acid (CH₃SO₂OH). However, while the tunneling splittings in chlorosulfonic and triflic acids are virtually identical, they differ significantly from that of methanesulfonic acid.

We present an experimental study of the dissociative excitation in the collision of helium ions with nitrogen and oxygen molecules for collision energy of $0.7\text{–}10.0$ keV. Absolute emission cross sections are measured and reported for the most pronounced nitrogen and oxygen atomic and ionic lines in vacuum ultraviolet ($80\text{–}130\mathrm{nm}$) and visible ($380\text{–}670\mathrm{nm}$) spectral regions. Remarkable similarities of the processes realized in He${}^{+}+$N₂ and He${}^{+}+$O₂ collision systems are observed. We present polarization measurements for He${}^{+}+$N₂ collision system.

The emission of excited dissociative products was detected using an improved high-resolution optical spectroscopy method. This method incorporates the retarding potential method and a high resolution electrostatic energy analyzer to precisely measure the energy of incident particles and the energy of dispersion. The improvement in the optical sensitivity allows us to measure the cross section on the order of 10⁻¹⁹ cm² or lower.

Standard thermodynamic functions of germane isotopologues ⁷⁰GeH₄, ⁷²GeH₄, ⁷³GeH₄, ⁷⁴GeH₄, and ⁷⁶GeH₄ are calculated in “harmonic oscillator – rigid rotator” and “anharmonic oscillator – oscillating non-rigid rotator” approximations and by the direct summation of the experimental energy values. To found the values of thermodynamic functions in the 200–700 K temperature range, approximation coefficients are determined by regression analysis. The isotope effect influence on the values of the standard isobaric heat capacity, entropy, enthalpy of heating, and the reduced isobaric-isothermal potential of germane is established. Limiting requirements for the accuracy of determining the spectral parameters for detecting the influence of the isotope effect on the thermodynamic functions and interatomic distances in the germane molecule are formulated.

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.

The rotationally resolved vibrational autodetachment spectrum of the H¹⁵NO^– anion has been observed in the region from 2932 to 3092 ${\mathrm{cm}}^{-1}$. ${{}^{r}R}_K\left(N\right)$ branches were observed for $K=4$ through 8, and two ${{}^{r}Q}_K\left(N\right)$ branches with $K=5$ and 6 were assigned. The ${{}^{r}Q}_5\left(N\right)$ branch of H¹⁴NO^– has also been identified. The new observations have allowed a rotational analysis of H¹⁵NO^– and have required a re-analysis of the previously observed spectrum of H¹⁴NO^–. The spectra are consistent with a ground state ($r_m^{\left(1\right)}$) geometry of $r_{\mathrm{NH}}=1.099\AA$, $r_{\mathrm{NO}}=1.330\AA$, and $\angle HNO={105.5}^{°}$, in good agreement with the results of Ellis and Ellison for the NO bond length and comparing well with recent theoretical treatments of this anion. The band has been reassigned as the $\left(0,2,0\right)-(0,0,0)$ band.

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.

Correct pressure broadening is essential for modelling radiative transfer in atmospheres, however data are lacking for the many exotic molecules expected in exoplanetary atmospheres. Here we explore modern machine learning methods to mass produce pressure broadening parameters for a large number of molecules in the ExoMol data base. To this end, state-of-the-art machine learning models are used to fit to existing, empirical air-broadening data from the HITRAN database. A computationally cheap method for large-scale production of pressure broadening parameters is developed, which is shown to be reasonably (69%) accurate for unseen active molecules. This method has been used to augment the previously insufficient ExoMol line broadening diet, providing air-broadening data for all ExoMol molecules, so that the ExoMol database has a full and more accurate treatment of line broadening. Suggestions are made for improved air-broadening parameters for species present in atmospheric databases.

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.

Recent advances in circumstellar metal chemistry and laser-coolable molecules have spurred interest in the spectroscopy and electronic properties of alkaline earth metal-bearing polyatomic molecules. We report the microwave rotational spectra of two members of this important chemical family, the linear magnesium-carbon chains MgC${}_4$H and MgC${}_3$N, detected with cavity Fourier transform microwave spectroscopy of a laser ablation-electric discharge expansion. The rotation, fine, and hyperfine parameters have been derived from the precise laboratory rest frequencies. These experimental results, combined with a theoretical quantum chemical analysis, confirm the recent identification of MgC${}_4$H and MgC${}_3$N in the circumstellar envelope of the evolved carbon-rich star IRC+10216. The spectroscopic data also provide insight into the structural and electronic properties that influence the metal-based optical cycling center in this unique class of laser-coolable polyatomics.