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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Research Projects

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n-C3H7CN  –  n-propyl cyanide

Investigators

  • hspm
  • wehres

Description

The propyl cyanides (PrCNs) are among the largest molecules which have been detected in star-forming regions. The straight-chain isomer n-PrCN was detected by some of us in the course of a molecular line survey of Sagittarius (Sgr) B2(N) at 3 mm (and shorter) using the IRAM 30 m telecope. The same group detected i-PrCN as the first branched alkyl molecule in a subsequent molecular line survey of Sgr B2(N) at 3 mm with ALMA (Atacama Large Millimeter/submillimeter Array). The sensitivity of the ALMA data suggested that we should be able to identify transitions pertaining to excited vibrational states of n-PrCN. ...more

Methods

Absorption Rotational Spectroscopy
Rotational spectroscopy is a key method to investigate molecules, radicals and ions. These species are capable of motions, in particular molecular rotation. If a permanent or induced dipole moment is existent, the species is called transient and the underlying energy states are quantized and accessible for electromagnetic waves. The energy distances between the rotational levels are such, that mostly the transition lines are in cm- (up to 30 GHz) and mm- (up to 300 GHz) wavelength range of the electromagnetic spectrum. Since the energies necessary to excite the rotational states are low, the typical temperatures in the ISM are sufficiently high for exiting these states (T = 5 K to > 100 K). The line frequencies of the transitions can be measured with great accuracy; this in turn gives precise molecular constants, which allows calculating reliable predictions of new molecular lines which helps to indentify new molecular species in space. Such line lists and constants for many species are available in our Cologne Database for Molecular Spectroscopy (www. CDMS.de).
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Instruments

MIDAS-COINS
With its exceptionally long absorption path, MIDAS-COINS is enhancing our sensitivity in the millimeter range since 2010.
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Recent Results

Spectra of n-PrCN were recorded between 36 and 70 as well as between 89 and 127 GHz. The lowest four vibrational states were analyzed for each conformer. The spectrum is particularly dense in regions of the anti conformer. Perturbations between v30 = 2 and v18 = 1 allowed us to determine their energy difference accurately. Analyses of spectral recordings extending to higher frequencies and of higher lying vibrational states are ongoing.

Section of the rotational spectrum of n-PrCN displaying mainly transitions of the anti conformer v30 = 1 (magenta asterisks) and v18 = 1 (green circles) as well as of the gauche conformer (g).
All four excited vibrational states of both conformers were subsequently identified in our ALMA data. The intensities of the lines were as expected from the model of the ground vibrational state assuming local thermodynamic equilibrium:

Sections of the ALMA spectral recordings toward Sgr B2(N2) displaying lines of the four excited vibrational states of the anti conformer.

Publications

External Links

Acknowledgments

  • The investigation has been funded by the Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Center 956 "Conditions and Impact of Star Formation", project B3, and through the Gerätezentrum "Cologne Center for Terahertz Spectroscopy".
  • Travel for A.W., D.L., and R.V. was partially supported by the French CNRS program “Physique et Chimie du Milieu Interstellaire” (PCMI).
  • O.H.W. acknowledges support from a Fulbright US Student Research Award.
  • R.T.G. is grateful for support from the NASA Astrophysics Theory Program through grant NNX11AC38G.
  • The following ALMA were used: ADS/JAO.ALMA#2011.0.00017.S and ADS/JAO.ALMA#2012.1.00012.S.