AB-INITIO THEORETICAL-STUDY OF DIPOLE-BOUND ANIONS OF MOLECULAR-COMPLEXES - WATER MOLECULE INHIBITS OR ENHANCES ELECTRON-AFFINITY OF N-METHYLAMINOADENINE

Ab initio calculations have been performed to determine the electron a ffinity of the water complex of N-methylaminoadenine (NMA). This compl ex has been chosen for this study because it can form three different isomeric structures with a water molecule hydrogen-bonded at three dif ferent NMA sites, and only two of these structures have sufficient dip ole moments to form dipole-bound states with an excess electron. In th e third structure, which according to the calculations should be the m ost stable form, the dipole moments of NMA and the water molecule oppo se each other resulting in an almost null dipole moment of the complex , so the complex has no ability to form a stable dipole-bound anion. T his determination offers an interesting possibility for;In experimenta l investigation of whether the NMA.H2O complex forms an stable anion. If such an anion is detected, it will mean that an electron attachment can increase the gas- phase concentration of the complex, which is th ermodynamically less stable in its neutral form.