Steric Effect in Threshold Photoionization Dissociations of Serine Conformers

Steric effect in the threshold dissociative ionizations of serine conformers [CH2OH-C\alphaH(NH2)-C\betaOOH] is revealed by high-level ab initio calculations combined with our newly developed infrared laser desorption / tunable VUV photoionization mass spectrometry. We find that near the ionization thresholds the C\alpha-C\beta and C\alpha-C bonds are selectively broken for the respective cationic conformers, yielding the different fragments. Novel dynamic processes, proton transfer and reorientation between the predissociative fragments, are involved in the threshold photoionization dissociations.