Rotationally resolved spectroscopy of jet-cooled NbMo

Rotationally resolved resonant two-photon ionization spectra of jet-cooled NbMo are reported for the first time. A vibronic spectrum of NbMo was recorded in the 17 300?22 300 cm?1 spectral region. Although the observed bands could not be grouped into electronic band systems, four excited vibronic levels with ?=2.5 and two excited levels with ?=3.5 were identified. The ground state of NbMo has been assigned as 2?5/2, deriving from a 1?21rr41?32?2 configuration of the valence electrons. Rotational analysis of six bands provides a ground state rotational constant of B0"=0.087 697(26) cm?1, corresponding to a bond length of r0"=2.008 09(30) ? for 93Nb98Mo. Correction for the effects of the spin-uncoupling operator changes the estimated bond length only slightly to r0"=2.008 02(30) ?. The experimentally determined value of r0" is compared to that predicted using previously determined multiple bonding radii of Nb and Mo. A comparison to the known diatomic molecules composed of group V and VI metal atoms is also made.