Rydberg and pulsed field ionization-zero electron kinetic energy spectra of YO

A spectroscopic study of the Rydberg states of YO accessed from particular rotational levels of the A (2)Pi(1/2), v=0 state has been combined with a pulsed field ionization, zero electron kinetic energy (PFI-ZEKE) investigation. The results provide accurate values of the ionization energy of YO, ionization energy I.E.(YO)=49 304.316(31) cm(-1) [6.112 958(4) eV], and of the rotational constant (and bond length) of the YO+ cation in its X (1)Sigma(+), v=0 ground state, B-0(+)=0.4078(3) cm(-1) [r(0)=1.7463(6) Angstrom]. The improved value of I.E.(YO) combined with the known ionization energy of atomic yttrium then leads to the result D-0(0)(Y-O)-D-0(0)(Y-O)=0.1041 +/- 0.0001 eV. Combining this result with the value of D-0(0)(Y+-O) obtained from guided ion beam mass spectrometry yields an improved value of D-0(0)(Y-O)=7.14 +/- 0.18 eV. The PFI-ZEKE spectra display an interesting channel-coupling effect so that all rotational levels with J(+)less than or equal to J(')(A)+0.5 are observed with high intensity, where J(+) is the angular momentum of the YO+ cation that is produced and J(')(A) is the angular momentum of the A (2)Pi(1/2) state that is reached when the first photon is absorbed. This is thought to result from the interaction between the dipole moment of the rotating YO+ core and the Rydberg electron, which can induce changes in l and J(+) subject to the dipolar coupling matrix element selection rule, Delta J(+)=+/- 1, Delta l=+/- 1. The channel-coupling mechanism also appears to induce an inverse autoionization process in which an unbound electron with a low value of l is captured either by its low-J(+) YO+ cation or by a second YO+ cation with the same value of J(+). This inverse autoionization process is extremely sensitive to the electron kinetic energy, leading to narrow peaks in the PFI-ZEKE spectrum which are only slightly broader than the laser linewidth employed for this study (0.25 cm(-1)). (C) 1999 American Institute of Physics. [S0021-9606(99)01335-5].