Heats of Formation of MHxCly (M = Si, P, As, Sb) Compounds and Main Group Fluorides from High Level Electronic Structure Calculations

The electronic spectrum of the jet-cooled stibino (SbH2) free radical

The òA₁-X̃²B₁ electronic transition of the jet-cooled stibino (SbH₂ and SbD₂) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH₃ or SbD₃) in high pressure argon at the exit of a pulsed molecular beam valve. SbH₂ exhibits only three LIF bands, assigned as 2₁ ⁰, 0₀ ⁰, and 2₀ ¹, with a fluorescence lifetime (τ), which decreases from ∼50 ns for 0⁰ to <10 ns for 2¹. LIF transitions to the 0⁰ (τ ∼ 2 µs), 2¹ (τ ∼ 400 ns), and 2² (τ ∼ 75 ns) upper vibronic states of SbD₂ were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r₀ ^″ = 1.724(2) Å, θ₀ ^″ = 90.38(7)° and r₀ ^' = 1.693(6) Å, θ₀ ^' = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm^-1) in SbH₂ and 12 quanta (6853 cm^-1) in SbD₂ were measured from dispersed fluorescence spectra. All indications are that SbH₂ undergoes a dissociative process at low vibrational energies in the excited electronic state.

Gas Phase Silver Thermochemistry from First Principles

Domain-based local pair natural orbital coupled cluster approach with single, double, and perturbative triple excitations, DLPNO-CCSD(T), has been applied within a framework of a reduced version of the reaction-based Feller-Peterson-Dixon (FPD) scheme to predict gas phase heats of formation and absolute entropies of silver inorganic and organometallic compounds. First, we evaluated all existing experimental data currently limited by thermodynamic functions of 10 silver substances (AgH, AgF, AgBr, AgI, Ag₂, Ag₂S, Ag₂Se, Ag₂Te, AgCN, AgPO₂). The mean average deviation between computed and experimental heats of formation was found to be 1.9 kcal/mol. Notably, all predicted heats of formation turned out to be within the error bounds of their experimental counterparts. Second, we predicted heats of formation and entropies for additional 90 silver species with no experimental data available, substantially enriching silver thermochemistry. Combination of gas phase heats of formation Δ H_f and entropies S° of AgNO₂, AgSCN, Ag₂SO₄, and Ag₂SeO₄ obtained in this work, with respective solid-state information, resulted in accurate sublimation thermochemistry of these compounds. Complementation of predicted Δ H_f with heats of formation of some neutrals and positive ions produced 33 silver bond strengths of high reliability. Obtained thermochemical data are promising for developing the concepts of silver chemistry. In addition, derived heats of formation and bond dissociation enthalpies, due to their high diversity, are found to be relevant for testing and training of computational chemistry methods.