Tomasz Motylewski

Gas-Phase Electronic Spectra of Carbon-Chain Radicals Compared with Diffuse Interstellar Band Observations

This paper compares laboratory gas-phase spectra of neutral and cationic linear carbon-chain radicals with astronomical diUuse interstellar band (DIB) spectra. The origin bands of the strong electronic tran- sitions of the studied species, (n \ 3¨6),

Cavity ring down spectroscopy on radicals in a supersonic slit nozzle discharge

A sensitive and generally applicable technique for direct absorption spectroscopy on electronic transitions of transient species in the gas phase is presented. The method is based on cavity ring down spectroscopy in a pulsed slit nozzle, incorporating a discharge in a high pressure supersonic expansion. The performance is demonstrated with spectra of the 000 origin band of the 2Π←X2Π electronic transition of the isoelectronic linear carbon chain radicals C6H and C6H2+. Rotationally resolved and rotationally cold spectra (Trot<15 K) have been obtained. The sensitivity of the technique is demonstrated for anions with a detection limit as low as 107 C2− molecules cm−3 for rovibrational transitions of the B2Σu+←X2Σg+ system.

The 2Π←X 2Π electronic spectra of C8H and C10H in the gas phase

The 2Π←X 2Π electronic transition of linear C8H/C8D and C10H/C10D has been detected in the gas phase. The carbon radical chains were produced at low temperatures in a pulsed slit nozzle, incorporating a discharge in a high pressure expansion. Cavity ring down spectroscopy is used as a sensitive technique to observe the band systems in absorption. The 000 band of the 2Π3/2←X 2Π3/2 electronic transition of C8H in the gas phase has its origin near 15 973.5 cm−1, whereas that of C10H is around 14 000 cm−1. Some transitions involving vibrational excitation in the upper 2Π electronic state have been also detected. These measurements were undertaken because carbon chains are among the appealing candidates as carriers of diffuse interstellar bands; the observed origin bands do not show matches with the hitherto reported wavelengths. However, these gas phase data now provide a firm basis for a specific astronomical search.

Rotationally resolved A2Πu←X2Πg electronic spectrum of tetraacetylene cation

Abstract The rotationally resolved A 2 Π u ← X 2 Π g electronic origin band spectrum of tetraacetylene cation (HC8H+) and its deuterated derivative (DC8D+) has been recorded in the gas phase, applying both frequency modulation spectroscopy in a liquid nitrogen cooled hollow cathode discharge and cavity ringdown spectroscopy in a supersonic planar plasma. The combined analysis of the rotational structure yields accurate molecular constants for the ground and electronically excited states as well as information on the molecular geometry.

The 1Πu← X 1Σg+ electronic spectrum of C5 in the gas phase

The origin and three vibronic bands of the 1Πu←X 1Σg+ electronic transition of linear C5 have been observed in the gas phase. The carbon chain is produced in a slit nozzle employing both discharge and ablation techniques. Cavity ring down spectroscopy is used to measure the electronic transition. The origin band is found at 510.94(1) nm, shifted 29 cm−1 to the red of the value in a neon matrix. Intramolecular processes lead to broadening and irregularities in the rotational structure. The relation to astronomical observations is discussed.

Cw cavity ring down spectroscopy in a pulsed planar plasma expansion

Acw cavity ring down spectrometer has been constructed with the aim to record electronic spectra of rotationally cold carbon chain radicals at high spectral resolution in direct absorption. The radicals are generated in a discharge of a high pressure gas pulse of acetylene in helium in a multilayer slit nozzle. Apassive cavity mode locking scheme is used to handle refractive index changes inside the cavity caused by gas pulse and plasma fluc

The 3Σu−←X 3Σg− electronic spectrum of linear C4 in the gas phase

The 3Σu−←X 3Σg− electronic absorption spectrum of linear C4 has been detected in the gas phase. The origin and several vibronic transitions have been recorded by means of cavity ring down spectroscopy through a supersonic planar plasma. The origin band is found at 26 384.9(2) cm−1 (∼379 nm). A partly rotationally resolved origin band spectrum yields a value of B0′=0.1570(5) cm−1 for the electronically excited 3Σu− state.

The A 3Σ−–X 3Σ− electronic transition of HC6N

A combined matrix and gas phase study is presented to identify the A 3Σ−–X 3Σ− electronic transition of the linear triplet isomer of HC6N and isotopic derivative DC6N. Absorption spectra have been observed in a 6 K neon matrix after mass selective deposition and in the gas phase by cavity ring down spectroscopy through a supersonic planar plasma. The band origin of the 000 A 3Σ−–X 3Σ− electronic transition of HC6N is determined to be at 21 208.60(5) cm−1, shifted ∼30 cm−1 to the blue of the neon matrix value. Rotational analysis indicates that the chain is slightly stretched on electronic excitation, yielding B0′=0.027 92(5) cm−1. Transitions to vibrationally excited levels in the upper A 3Σ− state are observed as well. The results are compared with a rotationally resolved spectrum of the 000 A 3Σu−–X 3Σg− electronic transition of the isoelectronic HC7H species.

Vibrationally excited state spectroscopy of radicals in a supersonic plasma

Abstract A plasma source based on a multilayer discharge geometry in combination with a time-of-flight REMPI experiment is used to study rotationally cold spectra of highly excited vibrational states of mass selected radicals. The rovibrational state distributions upon discharge excitation are characterised for the example of NO for ground state vibrational levels up to v″=18. Whereas rotational temperatures are lower than 50 K, a vibrational temperature of Tvib=6700±700 K is found.

Millimeter wave spectroscopy in a pulsed supersonic slit nozzle discharge

Abstract A Doppler-free technique for direct absorption spectroscopy of rotationally cold molecular ions in the millimeter wave range is presented. The method uses a double modulation technique, based on a simultaneous modulation of a frequency doubled microwave sweeper and a pulsed slit nozzle, incorporating a discharge in a high-pressure supersonic expansion. The performance is demonstrated with the observation of the hyperfine structure of the J =2←1 pure rotational transition of N 2 H + . Further perspectives of the method are discussed.