New electronic states in CH3, observed using multiphoton ionization

We report the first observation of the npe′ (2E′) and npa″2 (2A″2) electronic states in gas phase methyl radicals using the technique of resonance enhanced multiphonon ionization (REMPI). These previously unobserved states were identified in our REMPI spectrum as two-photon allowed resonance transitions leading to ionization. These electronic states arise from the excitation of the ground state electron in CH3 to np Rydberg orbitals. Transitions into these states from the ground 2A″2 electronic state are forbidden in one photon; however, they are allowed in a two-photon absorption. (AIP)