Abstract Submission Aldo Apponi

["Aldo Apponi" <aapponi@steffens.as.arizona.edu>]

NASA Laboratory Astrophysics Workshop 2006 Abstract Template

Title: 

Difficulties in Laboratory Studies and Astronomical Observations of 
Organic Molecules: Hydroxyacetone and Lactic Acid

Author(s):

Aldo J. Apponi, James J. Hoy, Matthew Brewster, and Lucy M. Ziurys
The University of Arizona, LAPLACE Astrobiology Center and Steward 
Observatory


Abstract:

Organic molecules in interstellar space likely play a role in prebiotic 
chemistry.  Hence, it is very important to properly identify the 
organic species present and to accurately evaluate their abundance.  
Owing to the rich molecular spectra found in many interstellar sources, 
accurate laboratory rest frequency measurements are crucial to 
accomplish these goals.

Two key molecules are hydroxyacetone and lactic acid.  A previous study 
on hydroxyacetone by Kattija-Ari and Harmony (1980) was not extensive 
enough to accurately predict even the A-state of this molecule, which 
has a methyl internal rotor.  The E-state proved even more difficult as 
they found the molecule to possess a very low barrier to internal 
rotation.  A more recent study by Braakman et al. (2005) provided rest 
frequencies for the A-state by measuring its spectrum at 3 mm and 1 mm, 
but they too reported that a definitive assignment of the E-state was 
proving difficult.  Just prior to that time, we started measuring the 
microwave spectrum of hydroxyacetone, which was critical for the 
assignment of the E-state.  We have now extended those measurements to 
cover the entire spectrum at 3 and 2 mm, where the strongest low-K 
interstellar transitions are predicted.  Using the methods described 
for fitting low-barrier molecules by Hougan and co-workers and a 
modified computer code provided by Kliener et al., we now have fitted 
rotational constants that reproduce the data to experimental accuracy 
in both the A- and E-states simultaneously.  The application of these 
methods will be described.

An extensive interstellar search has been conducted for hydroxyacetone 
based on these new laboratory results, as well as for lactic acid.  
Upper limits to the abundance of these species will be reported along 
with a discussion of problems in identifying these and other organic 
species owing to a high degree of spectral confusion.

Reference:

Kattija-Ari and Harmony, Inter. J. Quant. Chem., 14, 443 (1980)
Braakman et al., 60th International Symposium on Molecular 
Spectroscopy, Columbus, Ohio, Talk RA07