High Accuracy, ab initio Potential Energy Curves and Dipole Moment Functions for the X1Σ+ and a3Π Spin States of the CF+ Diatomic Molecule

Potential energy curves and dipole moment functions constructed using high accuracy, ab initio methods allow for an in-depth examination of the electronic structure of diatomic molecules. ab initio methods are invaluable especially for molecules that are difficult to synthesize and examine spectroscopically such as those found in the interstellar medium (ISM) where conditions allow for the longer lifetimes of lower stability molecules. The CF+ diatomic molecule is one such molecule that has been observed spectroscopically in the ISM. Previous experimental and theoretical work have examined different spectroscopic aspects of the CF+ molecule but the development of newer, more complete potential energy curves and dipole moment functions allow for even greater insight. We constructed both potential energy curves and dipole moment functions for the ground X1Σ+ and first excited a3Π states of CF+ for both 12C and 13C isotopologues. The potential energy curves were constructed using coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) at the complete basis set limit with corrections from full triple, quadruple, quintuple, and hextuple excitations within a finite-basis coupled cluster wavefunction as well as corrections from full configuration interaction and relativistic effects. Significant multireference character was identified in the electronic structure of CF+ which prompted the need for such high-level corrections to the PEC. Rovibrational wavefunctions were calculated using a vibrational Hamiltonian matrix which moves beyond the harmonic oscillator approximation. The equilibrium bond length, vibrational constant, and rotational constant were reproduced to within 0.00013 Å, 0.28 cm-1 and 0.00045 cm-1, respectively, of experimental values. Experimental transition energies from rovibrational spectra were reproduced with an error no larger than 0.63 cm-1. The triplet excited state (a3Π) was found to lie 4.808 eV (38774.9 cm-1) higher in energy with a slightly elongated bond length of 1.21069 Å. High accuracy rovibrational line lists for the 12C and 13C isotopologues for both the X1Σ+ and the excited a3Π state were generated.