Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies .
We wish to explore more organic molecules with increasing complexity in this region .
In particular , we have searched for one of the most complex organic molecules detected in space so far , ethyl formate ( C _ { 2 } H _ { 5 } OCHO ) .
This species is the next step in chemical complexity after the simplest member of esters ( methyl formate , CH _ { 3 } OCHO ) .
The mechanisms leading to its formation are still poorly known .
We have used high angular resolution ( \sim 1 . ^ { \prime \prime } 5 ) ALMA observations covering a large bandwidth from 214 to 247 GHz .
We have detected 82 unblended lines of C _ { 2 } H _ { 5 } OCHO ( 49 and 33 of the trans and gauche conformers , respectively ) .
The line images showed that C _ { 2 } H _ { 5 } OCHO arises mainly from the compact ridge and the hot core-southwest regions .
The derived rotational temperatures and column densities are 122 \pm 34 K , ( 0.9 \pm 0.3 ) \times 10 ^ { 16 } cm ^ { -2 } for the hot core-SW , and 103 \pm 13 K , ( 0.6 \pm 0.3 ) \times 10 ^ { 16 } cm ^ { -2 } for the compact ridge .
The comparison of spatial distribution and abundance ratios with chemically related molecules ( methyl formate , ethanol and formic acid ) indicates that C _ { 2 } H _ { 5 } OCHO is likely formed on the surface of dust grains by addition of CH _ { 3 } to functional-group radicals ( CH _ { 2 } OCHO ) derived from methyl formate ( CH _ { 3 } OCHO ) .