Gas-Phase Synthesis of Germanium Monosulfide (GeS, X¹Σ⁺) via the Elementary Reaction of Atomic Germanium (Ge, ³P) with Hydrogen Sulfide (H₂S, X¹A₁)

Germanium belongs to the carbon group in the periodic table; however, its chemical behavior sometimes differs from that of carbon, defying the isoelectronic rule proposed by Langmuir. One notable example is germanium monosulfide (GeS, X¹Σ⁺), where germanium exhibits remarkable stability in the +II oxidation state, unlike carbon in its monosulfide form. Germanium monosulfide (GeS, X¹Σ⁺) is a promising material, with applications ranging from optoelectronic devices to highly efficient semiconductors. Here, we report on the gas phase synthesis of germanium monosulfide (GeS) through the elementary reaction between ground-state atomic germanium (Ge, ³P) and hydrogen sulfide (H₂S, X¹A₁) via nonadiabatic reaction dynamics exploiting the single-collision approach in a crossed molecular beams machine. The integration of electronic structure calculations and experimental findings reveals that the reaction dynamics proceed via intersystem crossing (ISC) to produce singlet germanium monosulfide (GeS, X¹Σ⁺) and molecular hydrogen. This result provides an intricate reaction mechanism for the germanium-hydrogen sulfide system via germanium-sulfur bond coupling and demonstrates the "heavy atom effect" facilitated intersystem crossing yielding nearly exclusive singlet germanium monosulfide. This outcome also emphasizes that elementary reactions involving atomic germanium and hydrogen sulfide are quite different from those observed in the carbon-hydrogen sulfide or silicon-hydrogen sulfide systems.