The pure rotational spectrum of KSH (X(1)A') has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. This work is the first gas-phase experimental study of this molecule and includes spectroscopy of KSD as well. In the millimeter-wave system, KSH was synthesized in a DC discharge from a mixture of potassium vapor, H2S, and argon; a discharge-assisted laser ablation source, coupled with a supersonic jet expansion, was used to create the species in the FTMW instrument. Five and three rotational transitions in the range 3-57 GHz were recorded with the FTMW experiment for KSH and KSD, respectively, in the K(a) = 0 component; in these data, potassium quadrupole hyperfine structure was observed. Five to six transitions with K(a) = 0-5 were measured in the mm-wave region (260-300 GHz) for the two species. The presence of multiple asymmetry components in the mm-wave spectra indicates that KSH has a bent geometry, in analogy to other alkali hydrosulfides. The data were analyzed with an S-reduced asymmetric top Hamiltonian, and rotational, centrifugal distortion, and potassium electric quadrupole coupling constants were determined for both isotopolgues. The r0 geometry for KSH was calculated to be r(S-H) = 1.357(1) Å, r(K-S) = 2.806(1) Å, and θ(M-S-H) (°) = 95.0 (1). FTMW measurements were also carried out on LiSH and NaSH; metal electric quadrupole coupling constants were determined for comparison with KSH. In addition, ab initio computations of the structures and vibrational frequencies at the CCSD(T)/6-311++G(3df,2pd) and CCSD(T)/aug-cc-pVTZ levels of theory were performed for LiSH, NaSH, and KSH. Overall, experimental and computational data suggest that the metal-ligand bonding in KSH is a combination of electrostatic and covalent forces.
Pure rotational spectra of ScN, YN and BaNH in their 1 + ground electronic states were recorded in the 15 -55 GHz region using Fourier transform microwave/millimeter-wave spectroscopy. Hyperfine components arising from the J = 1 → 0 transitions were measured for all three molecules, and for YN, in the J = 2 → 1 line, as well. The 15 N isotopologues were also observed for the nitride species. The molecules were created in a supersonic jet by the reaction of metal vapor with ammonia using a discharge-assisted laser ablation source (DALAS). From these data, electric quadrupole and nuclear spin rotation hyperfine parameters were determined for the nitrogen nucleus in all species; metal hyperfine constants were additionally measured for ScN and YN. DFT calculations using the B3LYP functional were also performed to help aid in spectral assignments. For ScN, the scandium quadrupole coupling constant (eQq = 33.818(19) MHz) was found to be considerably smaller than in the corresponding halides, suggesting a different electronic structure. The nitrogen coupling constant for ScN is consistent with a more covalent molecule, perhaps even a diradical structure as well. In BaNH, a relatively small value of the nitrogen quadrupole coupling constant of eQq = 0.039 (11) MHz was determined, attributable to the non-terminal position of the nitrogen atom and the Ba-N triple bond.
Fourier transform microwave spectroscopy coupled with a discharge-assisted laser ablation source (DALAS) has been used to record the J = 1 → 0 pure rotational transitions of Sc 14 N, Sc 15 N, Y 14 N, Y 15 N, and Ba 14 NH (X 1 Σ +). Each species was synthesized by the reaction of the ablated metal with either NH 3 or 15 NH 3 in the presence of a DC discharge. For each species hyperfine structure was resolved. In the case of ScN and YN hyperfine parameters (quadrupole and nuclear spin-rotation) for the metal and nitrogen were determined and for BaNH the nitrogen quadrupole coupling constant was measured. These hyperfine constants are interpreted to gain insight into the metal-nitrogen bonding in each species. In addition, DFT calculations were performed to assist with the assignment of each spectrum and the characterization of the metal-nitrogen bond.
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