J/ApJ/791/L28 Gas-phase detection of c-C3H3+ (Zhao+, 2014)
Laboratory gas-phase detection of the cyclopropenyl cation (c-C3H3+).
Zhao D., Doney K.D., Linnartz H.
<Astrophys. J., 791, L28 (2014)>
=2014ApJ...791L..28Z 2014ApJ...791L..28Z (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: astrochemistry - ISM: molecules - methods: laboratory: molecular -
molecular data
Abstract:
The 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 3.19 µm 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 2013CPL...565..132Z, 2014JMoSp.296....1Z 2014JMoSp.296....1Z). In brief, the c-C3H3+
cations are generated by discharging a propyne (C3H4):He ∼ 1:200 gas
mixture in a multi-layer slit discharge nozzle (Motylewski & Linnartz
1999RScI...70.1305M 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-C3H3+ 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 <5x10-5cm-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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 49 130 Wavenumbers of the observed ro-vibrational
transitions of the ν4 fundamental band
of c-C3H3+
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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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
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Note (1): The heavily blended and some weak transition lines are set with
two times standard deviation in the least square fit.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 23-Mar-2017