MoP-12


THE GREAT DISTILLERY IN THE SKY

David A Fairley, Graham B I Scott, Colin G Freeman, Robert G A R Maclagan and Murray J McEwan

Department of Chemistry, University of Canterbury, Christchurch, New Zealand


Ethanol, C2H5OH, is one of the molecules observed in interstellar clouds. In the giant molecular cloud Sagittarius B2 which lies near the centre of our own galaxy there exists a quantity of ethanol roughly equivalent to 1000 times the mass of the Earth, which shows that interstellar gas clouds are distilleries of literally astronomical proportions. The radiatively stabilised ion-molecule association of H3O+ with C2H4 (1) followed by dissociative electron-ion recombination (2) has been proposed as a possible route to the formation of interstellar C2H5OH.

H3O+ + C2H4 ---> C2H5OH2+ + hv (1)
C2H5OH2+ + e ---> C2H5OH + H (2)

Experiments have been performed using a selected ion flow tube (SIFT) in which the ion product of the termolecular analogue of reaction (1) was reacted with the neutrals acrylonitrile, CH2CHCN, and 2-fluorotoluene, C7H7F. The observed rates and product ratios were compared with those obtained for the reactions of protonated ethanol, C2H5OH2+ and protonated dimethyl ether, (CH3)2OH+, with the same neutrals.

As an adjunct to the experimental study, ab initio calculations were performed on the C2H7O+ potential energy surface using the G2 procedure. Four stable structures were identified: protonated ethanol, C2H5OH2+, protonated dimethyl ether, (CH3)2OH+ and the electrostatic complexes C2H4···H···OH2+ and CH3+···HOCH3.

A summary of the experimental and theoretical results will be presented.