Thorium Monosilicide, ThSi: An Experimental and Theoretical Study

Area of Science:

• Quantum Chemistry
• Spectroscopy
• Materials Science

Background:

• The Thorium-Silicon (ThSi) molecule's electronic structure and properties are not fully understood.
• Investigating diatomic molecules like ThSi provides fundamental insights into chemical bonding and molecular behavior.

Purpose of the Study:

• To comprehensively investigate the electronic states and properties of the ThSi molecule.
• To determine the ground electronic state, spectroscopic constants, bond energy, and enthalpy of formation for ThSi.
• To evaluate the accuracy of various theoretical methods, including Density Functional Theory (DFT), for predicting ThSi properties.

Main Methods:

• High-level multireference and coupled-cluster computational methods with large basis sets.
• Calculation of potential energy curves (PECs), electron configurations, and spin-orbit coupling effects for 16 electronic states.
• Resonant two-photon ionization (R2PI) spectroscopy to measure the bond energy (D0).
• Density Functional Theory (DFT) calculations using 16 exchange-correlation functionals.

Main Results:

• Identified 16 electronic states of ThSi within 0.9 eV, with the ground state being a 1¹Σ⁺ state.
• Measured experimental bond energy (D0) of 3.146(4) eV, consistent with computed values.
• Derived an enthalpy of formation for gaseous ThSi, Δ_fH_0K^o(ThSi(g)), of 971.8(6.0) kJ/mol.
• Assessed DFT errors for D0, re, and ωe against experimental and coupled-cluster data.

Conclusions:

• The study provides a detailed theoretical and experimental characterization of the ThSi molecule.
• Computational results agree well with experimental measurements, validating the employed theoretical approaches.
• The findings contribute to a better understanding of the electronic spectrum and thermochemistry of ThSi.