Ethyl Formate, C2H5OCHO, in the Interstellar Medium

A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, C. Comito, and P. Schilke
reported on the
Increased Complexity in Interstellar Chemistry: Detection and Chemical Modeling of Ethyl Formate and n-Propyl Cyanide in Sagittarius B2(N)
Astron. Astrophys. 499, (2009) 215–232.
See also the MPIfR press release (in English; German version also available).
In the group of the complex molecules detected by radio astronomical means, ethyl formate, C2H5OCHO, and n-propyl cyanide are among the largest. They have been detected in the famous massive star-forming region Sagittarius B2(N) in the course of a molecular line survey in the 3 mm frequency domain with additional observations at 2 and 1 mm carried out with the IRAM 30 m radio telescope.
Aminoacetonitrile was detected earlier in the course of this molecular line survey.
At a rotational temperature of about 100 K, very many transitions of ethyl formate have non-negligible intensities. However, many of them are blended severely with emissions or absorptions of other molecules. Nevertheless, a considerable number of transitions of the lower energy anti-conformer are not or only slightly blended. Its column density in Sgr B2(N) is similar to that of formic acid, and about a factor of 15 lower than that of methyl formate.

The molecule was recently also identified in the Orion KL compact ridge region in the course of a molecular line survey carried out with the IRAM 30 m radio telescope.
B. Tercero, I. Kleiner, J. Cernicharo, H. V. L. Nguyen, A. López, and G. M. Muñoz Caro:
Discovery of Methyl Acetate and Gauche Ethyl Formate in Orion
Astrophys. J. 770, (2013) Art. No. L13.
Both conformers, anti and gauche, had about similar column densities, compatible with a kinetic temperature of 135 K. This agrees essentially with 150 K derived as rotational temperature of methyl acetate, which has a five times higher column density in this source than ethyl formate.

Ethyl formate is the second ester and the second formate to be detected in the ISM after methyl formate. The isomeric methyl acetate was also detected very recently.


Contributor(s): H. S. P. Müller; 04, 2009; 07, 2013