Analytic Empirical Potentials for all Stable Isotopologues of the Ground X(^1Σ^+) State of ZnO from Purely Rotational Measurements

We report eight new ultra-high precision (±5 kHz) measurements of purely rotational N(1←0) transitions in several vibrational states of all stable isotopologues of the ground X(11Σ+) -state of ZnO. Combined with previous high-resolution (±50 kHz) measurements of purely rotational transitions between higher rotational states for the same system, we are able to build analytic potentials for 64Zn16O, 66Zn16O, 67Zn16O, 68Zn16O, and 70Zn16O, that are in full agreement with all known spectroscopic measurements of the system. Despite there being absolutely no vibrational information, our empirical potentials are able to determine the size of the vibrational spacings and the bond lengths, each with a precision of more than two orders of magnitude greater than the most precise empirical values previously known. We then use the XDM method to calculate values for the C6, C8, and C10 long-range constants for this molecule, and use these to accurately anchor the long-range regions of the potentials, where no measurements have yet been performed. In the region lying between the short-range measurements and the long-range theory on which our potentials are based, our final analytic global potentials are in very good agreement with state of the art ab initio potentials. L. N. Zack, R. L. Pulliam, L. M. Ziurys, J. Mol. Spec., 256, 186-191 (2009).