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 2II1/2, 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?+, v=0 ground state, B0+=0.4078(3) cm21 [r0=1.7463(6) ?]. The improved value of I.E.(YO) combined with the known ionization energy of atomic yttrium then leads to the result D0 0 (Y+-O)2D0 0 (Y2O=0.1041?0.0001 eV. Combining this result with the value of D0 0 (Y+-O) obtained from guided ion beam mass spectrometry yields an improved value of D0 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+?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 2II1/2 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, ?J+=?1, ?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+1 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).