Narrow excitation features present on the [Ar]3d6 4s1 a6 D(J = 9/2 - 1/2) â† [Ar]3d5 4s 2 a6 S1/2 transitions of manganese atoms isolated in solid Kr are analyzed within the framework of weak crystal field splitting. Use of the Wp optical lineshape function allowed identification of multiple zero-phonon lines for individual spin-orbit J states of the a6D â† a6S transition recorded with laser-induced excitation spectroscopy. Excellent agreement exists between the predicted crystal field splitting patterns for the J levels of the a 6D state isolated in the Â«redÂ» tetravacancy site of solid Kr. The tetrahedral crystal field of the Â«redÂ» trapping site splits J > 3/2 levels of the a6DJ and a4D 7/2 states by approximately 30 cm-1. This report represents the first definitive evidence of crystal field splitting, induced by the weak van der Waals interactions between a neutral metal atom and the rare gasatoms surrounding it in a well defined solid state site. PACS: 31.70.Dk Environmental and solvent effects; 78.40.-q Absorption and reflection spectra: visible and ultraviolet; 78.55.-m Photoluminescence, properties and materials. Â© O. Byrne, M.A. Collier, M.C. Ryan, and J.G. McCaffrey, 2010.