J/ApJ/791/L28 Gas-phase detection of c-C_3_H_3_^+^ (Zhao+, 2014) ================================================================================ Laboratory gas-phase detection of the cyclopropenyl cation (c-C_3_H_3_^+^). Zhao D., Doney K.D., Linnartz H. =2014ApJ...791L..28Z (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Atomic physics Keywords: astrochemistry - ISM: molecules - methods: laboratory: molecular - molecular data Abstract: The cyclopropenyl cation (c-C_3_H_3_^+^) 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 {nu}_4_(C-H asymmetric stretching) fundamental band of c-C_3_H_3_^+^. The c-C_3_H_3_^+^ 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 3.19 {mu}m 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. Description: The experimental setup has been described in detail by Zhao et al. (2013CPL...565..132Z, 2014JMoSp.296....1Z). In brief, the c-C_3_H_3_^+^ cations are generated by discharging a propyne (C_3_H_4_):He ~ 1:200 gas mixture in a multi-layer slit discharge nozzle (Motylewski & Linnartz 1999RScI...70.1305M) in combination with a pulsed valve (General Valve, Series 9,2 mm orifice). The gas mixture is expanded with a backing pressure of ~7 bar through a 300umx3cm slit into a vacuum chamber. A pulsed negative high voltage (-600 V/300 mA) with a ~600 us duration is found to be optimum for c-C_3_H_3_^+^ production, is applied to the expanding gas mixture, and is set to coincide with the expanding gas pulse (~800 us). Continuous-wave cavity ring-down spectroscopy (cw-CRDS) is used to record spectra in direct absorption. The axis of the optical cavity is aligned parallel to and ~2 mm downstream of the slit nozzle throat. A single-mode cw optical parametric oscillator (Aculight), operating at ~3.15 um with a bandwidth <5x10^-5^cm^-1^, is employed as tunable IR light source. A hardware-based (boxcar integrator) multi-trigger and timing scheme recently reported by Zhao et al. (2013CPL...565..132Z) is used to apply cw-CRDS to the pulsed plasma. In the present experiment, typical ring-down time values are ~8-10 us, corresponding to a detection sensitivity, i.e., noise equivalent absorption, of up to ~2x10^-7^ per centimeter for the 3 cm long plasma jet. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 49 130 Wavenumbers of the observed ro-vibrational transitions of the {nu}_4_ fundamental band of c-C_3_H_3_^+^ -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 F8.3 cm-1 Obs Observed wavenumber 10- 15 F6.3 cm-1 o-c Obs. - Calc. wavenumber 17 I1 -- StdDev Standard deviation (1) 19- 26 A8 -- Assign Assignment 28- 29 I2 -- J' Upper state rotational quantum number J 31- 32 I2 -- K' Upper state quantum number K 34- 35 A2 -- l' Upper state l 37- 39 A3 -- USymm Upper state level symmetry 41- 42 I2 -- J" Ground state rotational quantum number J 44- 45 I2 -- K" Ground state quantum number K 47- 49 A3 -- LSymm Ground state level symmetry -------------------------------------------------------------------------------- Note (1): The heavily blended and some weak transition lines are set with two times standard deviation in the least square fit. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 23-Mar-2017