Vibronic structure of the ²Π_u ground electronic state of dicyanoacetylene cation revisited by PFI-ZEKE photoelectron spectroscopy and ab initio calculations

Abstract

The X⁺²Π_u ← X¹Σ⁺_g transition of dicyanoacetylene has been recorded for the first time using pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy. The analysis of the photoelectron spectrum allowed an accurate determination of the adiabatic ionisation potential of C₄N₂ (E_i, ad./hc = 95,479 ± 2 cm⁻¹) and a description of the vibrational structure of the electronic ground state of the cation which is affected by the Renner–Teller effect and the spin–orbit interaction. The spin–orbit coupling constant was measured as −52 ± 2 cm⁻¹. These results are supported by ab initio calculations performed at the complete active space self-consistent field and second-order perturbation theory levels of theory, with extrapolation to the complete basis set limit.

Keywords:

• dicyanoacetylene
• 2-butynedinitrile
• PFI-ZEKE PES
• Renner–Teller effect
• spin–orbit interaction
• ab initio calculations

Acknowledgements

The authors thank the CLUPS laser centre facility for provision of laser beam time. Barbara Cunha de Miranda and Christian Alcaraz acknowledge Prof. F. Merkt for providing the design of the PFI-ZEKE spectrometer and F. da Costa for its mechanical engineering. All the ab initio calculations presented in this work were performed on the Hydra and Vega (CECI) clusters at the ULB/VUB Computing Center.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Barbara Cunha de Miranda and Christian Alcaraz acknowledge funding by the CAPES-COFECUB program [number 525/06] (France–Brazil), the RTRA ‘Triangle de la Physique’ (project: ‘RADICAUX’) for financial support in the development of the PFI-ZEKE spectrometer. Jean-Claude Guillemin thanks the Centre National d’Etudes Spatiales (CNES) for financial support. Jacques Liévin thanks the Fonds National de la Recherche Scientifique de Belgique [I.I.S.N. 4.4504.10 project] for financial support.