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Description
Astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range of organic molecules in order to be able to identify them. Very accurate spectroscopic constants are obtained in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict with very high precision the frequencies of transitions that have not been measured in the laboratory. In this work, an experimental study and its theoretical analysis is presented for two ^18^O-methyl formate isotopologues in order to detect for the first time both isotopologues in Orion KL. The experimental spectra of both isotopologues of methyl formate have been recorded in the microwave and sub-mm energy range from 1 to 660GHz. Both spectra have been analysed by using the Rho-Axis Method (RAM) which takes into account the CH3 internal rotation. Spectroscopic constants of both ^18^O-methyl formate have been obtained with high accuracy. Thousands of transitions were assigned and others predicted, which allowed us to detect both species in the IRAM 30m line survey of Orion KL for the first time in the space.
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