High-resolution spectroscopy of He2+ using Rydberg-series extrapolation and Zeeman-decelerated supersonic beams of metastable He2

Recently, high-resolution spectroscopy of slow beams of metastable helium molecules (He₂^∗) generated by multistage Zeeman deceleration was used in combination with Rydberg-series extrapolation techniques to obtain the lowest rotational interval in the molecular helium ion at a precision of 18 MHz (Jansen et al., 2015), limited by the temporal width of the Fourier-transform-limited laser pulses used to record the spectra. We present here an extension of these measurements in which we have (1) measured higher rotational intervals of He₂⁺, (2) replaced the pulsed UV laser by a cw UV laser and improved the resolution of the spectra by a factor of more than five, and (3) studied M_J redistribution processes in regions of low magnetic fields of the Zeeman decelerator and shown how these processes can be exploited to assign transitions originating from specific spin-rotational levels (N^″,J^″) of He₂^∗ .