Dissociation of CH4 in a krypton matrix:: VUV spectra of atomic C and of the radical CH

Methane doped into Kr crystals was dissociated in situ using synchrotron radiation. Strong VUV absorption and emission lines could be attributed to atomic carbon by comparing them with its energy levels in the gas phase. Carbon atoms in the matrix are most efficiently excited within the triplet system (P-3 S-3, P-3 and D-3) and relax to the lowest excited quintet and singlet states before they return radiatively to the ground state. Very large blue shifted Rydberg states have to be invoked for this interpretation of the excitations. Other characteristic VUV spectra of dissociated methane in Kr matrix are attributed to the CH radical. Excitation into the D (II)-I-2 state is followed by emission either from the C (2)Sigma(+) State or from a higher energetic potential minimum which we tentatively assign to another (2)Sigma(+) State that is strongly modified in the matrix. Neither CH2 nor CH3 was observed in solid Kr.