Accurate first principles calculations on chlorine fluoride ClF and its ions ClF±

Abstract

The present work focuses on the first (lightest) of the six diatomic interhalogens, namely ClF and its ions ClF+ and ClF-, in an effort to better understand these interesting species. Toward this end, we have performed highly correlated all electron ab initio calculations of multireference (MRCI) and single-reference coupled-cluster calculations, employing quintuple and sextuple correlation consistent basis sets. Within the K - S ansatz, we have examined all 12 states of ClF correlating adiabatically with the first energy channel, all 23 states of ClF+ correlating with the first three channels, and three states out of four of ClF- correlating with the first two channels Cl- + F and Cl + F-. Full potential energy curves at the MRCI/quintuple zeta level have been constructed for 12, 21, and 3 states of ClF, ClF+, and ClF-, respectively. After correcting for core–subvalence and scalar relativistic effects, albeit small as expected, and spin–orbit interactions, most of our results are in excellent agreement with available experimental data. Some lingering questions have been definitely settled. Our final recommended binding energies (D0 in kcal/mol) and equilibrium bond distances (re in A ) for \( C1F\,\left( {X^1 \Sigma^+} \right),\,C1F^+ \,\left({X^2 \Pi } \right),\,and\,C1F^- \left({X^2 \Sigma^+} \right) \) are [60.35, 1.6284], [67.40, 1.5357], and [29.80, 2.151], respectively. The adiabatic electron affinity of ClF, \( C1F,\,C1F\left({X^1 \Sigma^+} \right) + e^- \to C1F^- \left({X^2 \Sigma^+} \right) \), is \( EA_{ad} = 2.25 \pm 0.001 \) eV about 0.6 eV smaller than the suggested experimental value which is certainly wrong.