Upper limits for stereoselective photodissociation of free amino acids in the vacuum ultraviolet region and at the C 1s edge.

We measured the total and partial ion yields of the two chiral amino acids alanine and serine in the gas phase both in the vacuum ultraviolet region and at the C(1s) edge using circularly polarized light. We did not detect any circular dichroism asymmetry larger than 1x10(-3). A similar measurement of fixed-in-space amino acids yielded an upper limit of 1x10(-2) for the stereoselective effect of circularly polarized light. The results obtained are relevant for quantitative models of stereoselective photodecomposition of amino acids that try to explain the homochirality of life