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 p
ulsed field ionization, zero electron kinetic energy (PFI-ZEKE) investigati
on. The results provide accurate values of the ionization energy of YO, ion
ization 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]. Th
e improved value of I.E.(YO) combined with the known ionization energy of a
tomic 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 fro
m 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-coup
ling 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 momen
tum 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 rul
e, Delta J(+)=+/- 1, Delta l=+/- 1. The channel-coupling mechanism also app
ears to induce an inverse autoionization process in which an unbound electr
on with a low value of l is captured either by its low-J(+) YO+ cation or b
y a second YO+ cation with the same value of J(+). This inverse autoionizat
ion process is extremely sensitive to the electron kinetic energy, leading
to narrow peaks in the PFI-ZEKE spectrum which are only slightly broader th
an the laser linewidth employed for this study (0.25 cm(-1)). (C) 1999 Amer
ican Institute of Physics. [S0021-9606(99)01335-5].