Precision bond lengths for Rydberg Matter clusters K19 in excitation levels n =4, 5 and 6 from rotational radio-frequency emission spectra

Several long series of up to 40 equally spaced lines are observed in the radio-frequency range 15–90?MHz that are attributed to stimulated emission from the electronically excited condensed matter called Rydberg Matter (RM). These frequencies are more than a factor of 1000 smaller than for most ordinary molecules, and if they did not agree with RM clusters they would indicate extremely large and heavy molecules that are unlikely to exist in the gas phase at room temperature. Theoretical predictions for RM clusters agree within 2% with the observed frequencies. Such clusters are planar, six-fold symmetric oblate rotors. The most prominent series with B?=?0.9292?±?0.0001?MHz (3.067?×?10^?5?cm^?1) agrees accurately with the theoretically predicted B value for the cluster K₁₉ in excitation level n?=?4, thus with a K–K bond length of 2.4074?nm. Two other prominent long series agree accurately with K₁₉ at n?=?5 and 6, with bond lengths of 3.804 and 5.518?nm, respectively. The ratio between the interatomic distance and the electron orbit radius for n?=?4 is found to be 2.8433?±?0.0003, a considerable improvement in precision over the theoretical value of 2.9.