LABORATORY GAS-PHASE DETECTION OF THE CYCLOPROPENYL CATION (c-C ₃ H ₃ ⁺ )

Abstract

<p>\n\tThe cyclopropenyl cation (c-C3H3 +) is the smallest aromatic hydrocarbon molecule and considered to be a pivotal intermediate in ion–molecule reactions in space. An astronomical identification has been prohibited so far, because of a lack of gas-phase data. Here we report the first high resolution infrared laboratory gas-phase spectrum of the ν4 (C–H asymmetric stretching) fundamental band of c-C3H3 +. The c-C3H3 + cations are generated in supersonically expanding planar plasma by discharging a propyne/helium gas pulse, yielding a rotational temperature of ∼35 K. The absorption spectrum is recorded in the 3.19μm region using sensitive continuous-wave cavity ring-down spectroscopy. The analysis of about 130 ro-vibrational transitions results in precise spectroscopic parameters. These constants allow for an accurate comparison with high-level theoretical predictions, and provide the relevant information needed to search for this astrochemically relevant carbo-cation in space.</p>