Trends in alkali metal hydrosulfides: A combined Fourier transform microwave/millimeter-wave spectroscopic study of KSH ($\tilde X^1 A^\prime $X̃1A′)

Abstract

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.

Examining transition metal hydrosulfides: The pure rotational spectrum of ZnSH (X̃2A′)

“…26 The bond length does not increase significantly for CuSH because of the energy gained by pairing electrons. The sulfur-hydrogen bond distance of 1.351(3) Å in ZnSH is comparable to that in CuSH, LiSH, NaSH, and KSH, 20,21,24,26 which all fall in the range r(S− −H) ∼ 1.353-1.357 Å (see Table III). The same bond length in H 2 S is slightly shorter at 1.335 (1) Å 38 and is likely a result of less steric hindrance by the hydrogen as opposed to the larger metal atoms.…”

“…Alkali and alkaline earth MSH species all show similarly bent structures, including LiSH, NaSH, KSH, MgSH, CaSH, SrSH, and BaSH, as does AlSH. [18][19][20][21][22][23][24][25] The MSH series have bond angles typically ranging from 89 • to 95 • , more comparable to that of H 2 S, suggesting that the bond to the metal occurs primarily through sulfur p orbitals. For transition-metal hydrosulfides, only CuSH (X 1 A ) has thus far been investigated spectroscopically.…”

Theoretical characterization of the LiSH potential energy surface

“…For LiSH, the large active space was built with 3s, 3p atomic orbitals (AOs) of the sulfur atom, 2s, 3s AOs of the lithium atom, and 1s atomic orbital of the hydrogen atom. That is, 13 valence electrons were distributed into 8 molecular orbitals (MOs), being denoted as CAS (8,13). The two smallest active spaces were also tested in our exploratory calculations: QUARKS: Brazilian Electronic Journal of Physics, Chemistry and Material Science CAS (6,6) and CAS (8,8).…”

“…That is, 13 valence electrons were distributed into 8 molecular orbitals (MOs), being denoted as CAS (8,13). The two smallest active spaces were also tested in our exploratory calculations: QUARKS: Brazilian Electronic Journal of Physics, Chemistry and Material Science CAS (6,6) and CAS (8,8). However, these reference spaces did not prove to be satisfactory for the excited states, including a correct behavior of the asymptotic limits.…”

Multivalent optical cycling centers in polyatomic molecules

“…Typical approaches to gas-phase synthesis involve Nd:YAG laser ablation of a solid metal target, followed by the introduction of a gas-phase precursor via a heated capillary to produce the desired target species. For instance, thiol compounds with alkali [168][169][170], alkaline earth [171][172][173][174], (post-)transition metal centers [175,176] -including aluminum [177] -(MSH) are routinely produced in the gas phase via evaporation or ablation of solid metals in the presence of H 2 S gas. This method should be readily extendable to syntheses of MSH molecules with p-block metals.…”