IR–UV ion-dip spectroscopy of N-phenyl formamide, and its hydrated clusters

IR–UV ion-dip spectroscopy has been used to study N-phenylformamide and its hydrated clusters in the ground and excited (S1) electronic states. Their NH stretch bands readily differentiate cis (3441 cm−1) and trans (3463 cm−1) isomers. Clusters of trans-N-phenylformamide with 1 or 2 water molecules show nearly equal preference for binding to the NH and CO sites. A further cluster is assigned in which a chain of four water molecules form an H-bonded bridge between NH and CO. Its vibrational spectrum is characterised by broad, intense and red-shifted bands resulting from strong cooperative effects and distribution of vibrational motion along the H-bonded chain.