(2+1) resonance-enhanced ionization spectroscopy of a state-selected beam of OH radicals

A state-selected beam of hydroxyl radicals is generated using a pulsed discharge source and hexapole field. The OH radicals are characterized by resonance-enhanced multiphoton ionization (REMPI) spectroscopy via the nested D (2)Sigma(-) and 3 (2)Sigma(-) Rydberg states. Simplified spectra are observed from the selected vertical bar M-J vertical bar=3/2 component of the upper Lambda-doublet level of the lowest rotational state (J=3/2) in ground (v=0) and excited (v=1-3) vibrational levels of the OH X (2)Pi(3/2) state. Two-photon transitions are observed to the D (2)Sigma(-)(v(')=0-3) and 3 (2)Sigma(-)(nu(')=0,1) vibronic levels, extending previous studies to higher vibrational levels of the Rydberg states. Spectroscopic constants are derived for the Rydberg states and compared with prior experimental studies. Complementary first-principle theoretical studies of the properties of the D (2)Sigma(-) and 3 (2)Sigma(-) Rydberg states [see M. P. J. van der Loo and G. C. Groenenboom, J. Chem. Phys. 123, 074310 (2005), following paper] are used to interpret the experimental findings and examine the utility of the (2+1) REMPI scheme for sensitive detection of OH radicals. (c) 2005 American Institute of Physics.