Gas-phase vibrational spectroscopy of the dysprosium monoxide molecule and its cation.

Rotationally resolved vibrational spectra of DyO and DyO + in a molecular beam are obtained by IR excitation from the X8 ground state and from high- n Rydberg states of DyO using an infrared free electron laser. Vibrational excitation is detected either by resonance enhanced multiphoton ionisation from X8( v = 1) or by autoionisation of Rydberg states converging to DyO + ( v = 1). For most heavy molecules, the large spectral width of an infrared free electron laser does not allow for rotational resolution. In DyO and DyO + the P, Q, and R transitions can be resolved due to the high angular momentum in their ground states. For 164 DyO a vibrational constant of ω e = 847.5(2) cm -1 and a vibrational anharmonicity of ω e χ e = 2.9(1) cm -1 are deduced. For the 161 DyO + cation a transition frequency of Δ G 1/2 = 907(1) cm -1 is found.