Spectroscopic Characterization of the Ground and Low-Lying Electronic States of Ga2N via Anion Photoelectron Spectroscopy.

Anion photoelectron spectra of Ga2N− were measured at photodetachment wavelengths of 416nm(2.978eV), 355nm(3.493eV), and 266nm(4.661eV). Both field-free time-of-flight and velocity-map imaging methods were used to collect the data. The field-free time-of-flight data provided better resolution of the features, while the velocity-map-imaging data provided more accurate anisotropy parameters for the peaks. Transitions from the ground electronic state of the anion to two electronic states of the neutral were observed and analyzed with the aid of electronic structure calculations and Franck-Condon simulations. The ground-state band was assigned to a transition between linear ground states of Ga2N−(XΣg+1) and Ga2N(XΣu+2), yielding the electron affinity of Ga2N, 2.506±0.008eV. Vibrationally resolved features in the ground-state band were assigned to symmetric and antisymmetric stretch modes of Ga2N, with the latter allowed by vibronic coupling to an excited electronic state. The energy of the observed excited neutral state agrees with that calculated for the AΠu2 state, but the congested nature of this band in the photoelectron spectrum is more consistent with a transition to a bent neutral state

The offset dependent behavior of narrow optical emission features in the Red Rectangle proto-planetary nebula

Context. The Red Rectangle proto-planetary nebula provides a unique laboratory to study the physical conditions and chemical processes in stellar outflows. Snapshots of the ongoing chemical evolution are obtained by monitoring spectra as function of the offset from the central star. Aims. The focus in this study is on the characterization of narrow optical emission features, that are superimposed on top of extended red emission (ERE). The primary aim is to provide a two-dimensional catalogue of these features for offsets varying from 3 '' to 20 '' from the central star. Methods. Medium resolution emission spectra for this catalogue have been obtained through optical long-slit measurements using the New Technology Telescope (EMMI-NTT) in La Silla, Chile. Results. The recorded spectra cover the range between 5550 and 6800 angstrom. A complete overview of the central band positions and bandwidths (FWHMs) is provided for both stronger (previously reported) and weaker narrow features. Only some bands are omnipresent in the nebula outflows and other bands only appear further away from the central star. Conclusions. The optical emission bands show intensity variations over the nebula. We suggest that these variations reflect a spatially resolved photochemistry where larger species are photolysed, producing daughter molecules which may be the carriers of the optical emission bands

A coincidence between a hydrocarbon plasma absorption spectrum and the lambda 5450 DIB

The aim of this work is to link the broad lambda 5450 diffuse interstellar band (DIB) to a laboratory spectrum recorded through an expanding acetylene plasma. Cavity ring-down direct absorption spectra and astronomical observations of HD 183143 with the HERMES spectrograph on the Mercator Telescope in La Palma and the McKellar spectrograph on the DAO 1.2 m Telescope are compared. In the 543-547 nm region a broad band is measured with a band maximum at 545 nm and FWHM of 1.03(0.1) nm coinciding with a well-known diffuse interstellar band at lambda 5450 with FWHM of 0.953 nm. A coincidence is found between the laboratory and the two independent observational studies obtained at higher spectral resolution. This result is important, as a match between a laboratory spectrum and a - potentially lifetime broadened - DIB is found. A series of additional experiments has been performed in order to unambiguously identify the laboratory carrier of this band. This has not been possible. The laboratory results, however, restrict the carrier to a molecular transient, consisting of carbon and hydrogen.Comment: 6 pages, 3 figures, accepted for publication in A&

Electronic spectra and structure of the non-linear carbon chain C9H3

Two electronic bands at ∼18 881 and ∼18 920 c

Rotational spectroscopy of the two higher energy conformers of 2-cyanobutane

We present high-resolution rotational spectroscopy of the two higher energy conformers of 2-cyanobutane (C4H9CN). We analysed spectra starting from 12 to 27 GHz using the Cologne chirpedpulse (CP) Fourier transform microwave spectrometer, which we discuss for the first time. Spectra between 36 and 402 GHz were also recorded by means of frequency modulated (FM) absorption spectroscopy. In addition, quantum chemical calculations were performed assisting the assignments. Furthermore ground state energies of the conformers have been calculated and subsequent experimental analysis of line intensities have been performed. This study provides precise spectroscopic constants, relative energies and vibrational frequencies of the three conformers for the search of 2-cyanobutane in star-forming regions. Additionally, this molecule poses an interesting case to test our knowledge of the abundance of chiral molecules in space. (C) 2018 Published by Elsevier Inc

Vibronic spectrum of 15N16O2 between 415 and 440 nm.

The time gated laser induced fluorescence (LIF) excitation spectrum of adiabatically coole

C2 emission features in the Red Rectangle: A combined observational laboratory study

Context. The Red Rectangle proto-planetary nebula (HD 44179) is known for a number of rather narrow emission features superimposed on a broad extended red emission (ERE) covering the 5000-7500 angstrom regime. The origin of these emission features is unknown. Aims. The aim of the present work is to search for potential carriers by combining new observational and laboratory data. This also allows to interpret spectral emission features in terms of actual physical conditions like temperature and density constraints and to trace chemical processes in the outflows of the Red Rectangle. Methods. Observational spectra have been obtained with the EMMI-NTT at offsets of 3 '', 6 '', 7 '', 11 '', 16 '' and 20 '' distance to the central star HD 44179. The spectra are compared to the outcome of a time-gated laser induced fluorescence laboratory study of an expanding acetylene plasma using a special supersonic pin-hole discharge source. With this set-up the hydrocarbon chemistry in the Red Rectangle nebula is simulated under laboratory controlled conditions. The plasma source has the unique feature to generate electronically and vibrationally excited species at low rotational temperatures. The comparison is facilitated by a simple model for fluorescent emission in the nebula. Results. Two of the astronomically observed narrow emission bands can be assigned as originating from unresolved rovibronic progressions within the d(3)Pi(g) -> a(3)Pi(u) Swan system of the C-2 radical. The band appearance corresponds to a rotational temperature between 200 and 1000 K. The emission is driven by absorption in the C-2 Phillips bands followed by intersystem crossing from the singlet to the triplet state and pumping in the Swan bands. Conclusions. These observations imply an active (photo) chemistry in the ejecta of the Red Rectangle

Search for DIBs in Emission: MWC 922 - The Red Square Nebula

This work focusses on MWC 922, the central object in the Red Square Nebula. We obtained low and medium resolution spectra of both, the central object and the surrounding nebula, using the DIS and TSpec spectrograph. The spectra show the whole spectral range between ~3 500 Å up to ~25 000 Å. The central object shows a plethora of emission lines, including many Fe II and forbidden Fe [II] lines. Here, we present the inventory of the emission lines of the central object, MWC 922. Future work will comprise the identification of the nebula emission lines by using newly obtained X-Shooter spectra. That way we want to gain further insight into the physical and chemical conditions in this environment. A comparison of the Red Square to the Red Rectangle Nebula is anticipated and will guide our search for DIBs in emission

A laboratory heterodyne emission spectrometer at submillimeter wavelengths

We present first results on a newly built broadband emission spectrometer for the laboratory making use of a double sideband (DSB) heterodyne receiver. The new spectrometer is perfectly suited for highresolution emission spectroscopy of molecules of astrophysical importance. The current SIS receiver operates at RF frequencies between 270 and 390 GHz, coincident with Band 7 of the ALMA telescope. The instantaneous bandwidth is 5 GHz (DSB). In this work the full spectrometer and its components are described. Its performance, in particular its sensitivity, stability, reproducibility and systematic errors, is characterized in detail. For this purpose very broad band emission spectra of methyl cyanide have been recorded and compared to theoretical spectra. Isotopic variants are found in natural abundance and features attributed to vibrationally excited species are all recorded in the same spectrum. The performance of the new spectrometer is compared extensively to that of a traditional FM-absorption spectrometer and to recent versions of chirped-pulse spectrometers operated in the mm-wave regime. Further applications and future advancements of the current instrument are discussed