Theoretical Estimation of the Radiative Association Rate between Mg⁺ and HCN(X¹Σ⁺)

Area of Science:

• Astrochemistry
• Quantum Chemistry
• Computational Physics

Background:

• The formation of molecules like magnesium cyanid (MgCN) in the gas phase of circumstellar envelopes around evolved stars is crucial for understanding chemical evolution.
• The radiative association of hydrogen cyanide (HCN) with magnesium ions (Mg+) is hypothesized as the initial, rate-limiting step in MgCN formation.

Purpose of the Study:

• To evaluate the radiative association rate of HCN with Mg+ using quantum mechanical methods.
• To validate the proposed MgCN formation pathway in the interstellar medium.

Main Methods:

• An analytical potential energy surface model was developed from extensive *ab initio* calculations.
• Bound states of the complex were computed for low total angular momentum values.
• The J-shifting approximation was applied to solve the system's driven equations for the radiative association rate.

Main Results:

• The study successfully computed the radiative association rate of HCN with Mg+.
• The J-shifting approximation provided a viable alternative to computationally intensive close-coupling methods.
• Results were compared with those from a statistical approach, showing good agreement.

Conclusions:

• The calculated radiative association rate supports the proposed mechanism for MgCN formation in evolved star envelopes.
• The findings contribute to a better understanding of molecular complexity in astrophysical environments.
• The employed quantum methods and approximations are validated for similar astrochemical studies.