Intermolecular interaction in an open-shell pi-bound cationic complex: IR spectrum and coupled cluster calculations...

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• The acetylene cation (C2H2+) is a key species in astrochemistry and plasma physics.
• Understanding its interactions with noble gases like argon (Ar) is crucial for modeling complex chemical environments.

Purpose of the Study:

• To characterize the intermolecular potential energy surface (PES) of the Ar-C2H2+ complex.
• To investigate the structural and vibrational properties of the complex using experimental and theoretical methods.

Main Methods:

• Infrared photodissociation (IRPD) spectroscopy was employed to probe the vibrational modes of the complex.
• High-level quantum chemical calculations, including coupled cluster methods, were used to determine the PES and predict spectral properties.
• Rovibrational energy levels were calculated using a discrete variable representation-distributed Gaussian basis method.

Main Results:

• The IRPD spectrum analysis confirms a vibrationally averaged T-shaped structure for Ar-C2H2+.
• The antisymmetric CH stretching fundamental (nu(3)) exhibits a blueshift of 16.7 cm(-1) upon complexation.
• The intermolecular PES features a global pi-bound minimum and two shallow H-bound side wells.
• Effective spectroscopic constants were determined for the vibrational ground state.

Conclusions:

• The study provides a detailed characterization of the Ar-C2H2+ intermolecular potential energy surface.
• The observed blueshift indicates that vibrational excitation slightly weakens the interaction between Ar and C2H2+.
• The findings contribute to a deeper understanding of non-covalent interactions involving molecular cations.