Energy and spectroscopic parameters of neutral and cations isomers of the CnH2 (n = 2–6) families using high‐level ab‐initio approaches

• Published in: Journal of computational chemistry 2024-12, Vol.45 (32), p.2793-2804
• Main Authors: Díaz Soto, Lenin J., Oliveira, Ricardo R., Baptista, Leonardo, Silveira, Enio F., Nascimento, Marco Antonio Chaer
• Format: Article
• Language: English
• Subjects: ab initio F12 method; Banded structure; Cations; Charge distribution; CnH2 isomers; Desorption; Diffuse interstellar bands; Energy distribution; Isomers; Mass spectrometry; PDMS; Species diffusion; spectroscopic parameters; Topology
• ISSN: 0192-8651; 1096-987X; 1096-987X
• DOI: 10.1002/jcc.27485

Cationic species, previously detected from ion‐induced desorption of solid methane by plasma desorption mass spectrometry (PDMS), and neutral species, are investigated using high‐level ab‐initio approaches. From a set of 25 cationic and 26 neutral structures belonging to CnH2 (n = 2–6) families, it was obtained the energy, rotational constants, harmonic vibrational frequency, charge distribution and excitation energies. The ZPVE‐corrected energies, at CCSD(T)‐F12; CCSD(T)‐F12/RI/(cc‐pVTZ‐F12, cc‐pVTZ‐F12‐CABS, cc‐pVQZ/C) (n = 2–5) and CCSD(T)/cc‐pVTZ (n = 6) levels, reveal that the topology of the most stable isomer vary with n and the charge. Out of 674 harmonic frequencies, those with maximum intensity are generally in the 3000–3500 cm−1 range. Analysis of 169 vertical transition energies calculated with the EOM‐CCSD approach, suggest three C6H2 species as potential carriers of the diffuse interstellar bands (DIB). Systematic comparison of properties between neutral and cationic species can assist in the structural description of complex matrices. Based on the results of coupled‐cluster methodologies, the cationic species of the CnH2 (n = 2 – 6) families, previously detected in the ion‐induced desorption of solid methane, were identified. The calculated harmonic vibrational frequencies, vertical transition energies, and oscillator strengths allow for distinguishing between the neutral and cationic CnH2 species. Reliable computational data can facilitate the interpretation of interstellar observations.