Three-photon absorption spectroscopy:: the L(1Φ3) and m(3Π1) states of HCl and DCl

Analysis of (3 + 1) REMPI room temperature spectra by use of three-photon absorption modelling allowed, for the first time, identification and characterization of Omega = 3, Phi states (L((1)Phi(3))) in HCl and DCl and of the m((3)Pi(1)) state in DCl. Simulation analyses and determination of isotope shifts allowed evaluation of vibrational and rotational spectroscopic parameters for both states and both molecules. The mechanism of three-photon absorption in the m((3)Pi(1)) X((1)Sigma(+)) transition is discussed.