LABORATORY ROTATIONAL SPECTRUM OF l -C 3 H + AND CONFIRMATION OF ITS ASTRONOMICAL DETECTION

The rotational spectrum of l-C3H+ has been measured in the millimeter-wave band in a 4 K cryogenic ion trap apparatus employing a novel mass-selective action spectroscopy method based on light induced reactions (LIR). Line positions of four rotational transitions (J = 1-2 up to J = 4-5) were observed with a relative precision of 3 × 10–7. The experimental transition frequencies and derived spectroscopic constants agree with those from recent astronomical observations, and unambiguously confirm the detection of this astrochemically relevant carbocation in the Horsehead photodissociation region and toward Sgr B2(N).