K. CHEN, Department of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC.
To explore the possibility of K -level resolved, 2+1 resonance-enhanced multiphoton ionization (REMPI) processes of the methyl radical, the two-photon absorption selection rules and rotational line strengths of the 301 and 401 vibronic bands of the transition np X ( n =3 or 4) were reported. Stringent selection rules, which were imposed upon these two-photon transitions, are the initial K ''=3 p ( p =0,1,2,...), K =\pm2, U =\pm3 and N =0,\pm1,\pm2 ( O , P , Q , R , and S branches). The previously assigned 222 vibronic band of the methyl radical should be studied by the REMPI with a better spectral resolution and analyzed by the newly derived two-photon absorption selection rules and rotational line strength formulas.