Rovibrational states of ClHCl⁻ isotopologues up to high J: a joint theoretical and spectroscopic investigation

Explicitly correlated coupled cluster theory at the CCSD(T*)-F12b level (T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys., 2007, 127, 221106) and two precise spectroscopic parameters (K. Kawaguchi, J. Chem. Phys., 1988, 88, 4186) were used to construct an accurate near-equilibrium analytical potential energy function (PEF) for the highly anharmonic centrosymmetric hydrogen-bonded complex ClHCl⁻ (R_e = 3.1153 Å). From variational calculations with that PEF, a large number of rovibrational energies of different isotopologues up to high values of the rotational quantum number J was obtained. Theory helped with the assignment of lines observed by IR diode laser spectroscopy in the ν₁ + ν₃ combination band of ³⁵ClH³⁵Cl⁻ and ³⁷ClH³⁵Cl⁻ and enabled us to elucidate rather subtle patterns of rovibrational interactions. Furthermore, transition dipole moments were predicted and analysed as well as unusual isotopic effects.