ZrFe, a sextuply-bonded diatomic transition metal?

Diatomic ZrFe has been spectroscopically investigated for the first time, with the optical spectrum recorded in the range from 13890 cm(-1) to 18870 cm(-1). In the region from 13890 to 17500 cm(-1), a single exceptionally weak vibrational progression is found. Band origins, excited state vibrational frequencies and anharmonicities, excited state lifetimes, and the ground state vibrational interval, ΔG"(1/2), are reported for the five most abundant isotopomers. For the most abundant species, (90)Zr(56)Fe (47.2%), these values are: T(0) = 13931.9(1.2) cm(-1), ω'(e) = 325.05(54) cm(-1), ω'(e)x'(e) = 1.589(40) cm(-1), and ΔG"(1/2) = 452.2 cm(-1). Rotationally resolved studies have revealed ground and excited state rotational constants and Ω values, bond lengths and rotation-vibration constants, giving B(0)" = 0.138786(30) cm(-1) and r(0)" = 1.87685(20) Å for (90)Zr(56)Fe. The ground state and all observed excited states have Ω = 0. On the basis of the short bond length, the ground state of ZrFe is assigned as a nominally sextuply bonded (1)Σ(+) (Ω = 0(+)) state deriving from the 1σ(2)1π(4)2σ(2)1δ(4) electronic configuration. Above 18000 cm(-1), the spectrum becomes much more intense and congested, indicating the onset of electronically allowed transitions in this region.