A variety of theoretical methods have been applied to the
state of CP. In order to ascertain the degree of convergence in the computed properties with respect to the basis set, a series of correlation-consistent basis sets, ranging up to the quintuple zeta level, were used. For some properties the convergence was sufficiently uniform that a simple analytical expression could be fitted to the available theoretical data, so as to permit an estimate of the complete basis set limit. The set of observables that was examined includes spectroscopic constants
, rotational transition energies, one-electron properties (
, Q, etc), vibrational transition energies, vibrational dipole moments and others. The vibrational energies were compared to experiment, as well as to numerical results simulating experiments based on the Rydberg - Klein - Rees - Vanderslice method. Transition Einstein A coefficients, transition wavenumbers and integrated absorption intensities for a selected set of rotational lines in the R branch of selected vibrational bands have been computed using a multireference, configuration- interaction potential energy surface which included a correction for higher-order excitations. The theoretical results are analysed in the light of recent stellar and laboratory-frame observations. Finally, the vibrational lifetimes (with and without rotational dependence) have been derived for the first ten vibrational levels using the latter above-mentioned potential surface. These lifetimes could be measured with existing experimental technologies.