Vibrational Spectroscopy of the Dehydrogenated Uracil Radical by Autodetachment of Dipole-Bound Excited States of Cold Anions

Molecules with large enough dipole moments can bind an electron by the dipole field, which has little effect on the molecular core. A molecular anion can be excited to a dipole‐bound state, which can autodetach by vibronic coupling. Autodetachment spectroscopy of a complex anion cooled in a cryogenic ion trap is reported. Vibrational spectroscopy of the dehydrogenated uracil radical is obtained by a dipole‐bound state with partial rotational resolution. Fundamental frequencies for 21 vibrational modes of the uracil radical are reported. The electron affinity of the uracil radical is measured accurately to be 3.4810±0.0006 eV and the binding energy of the dipole‐bound state is measured to be 146±5 cm−1. The rotational temperature of the trapped uracil anion is evaluated to be 35 K. The vibrational spectrum of the dehydrogenated uracil radical has been measured by autodetachment from dipole‐bound states of cold deprotonated uracil anions. The spectrum shows observed rotational profiles (blue circles) for mode ν16 at 577 cm−1 (c‐type) and mode ν24 at 615 cm−1 (b‐type), in comparison with the simulated rotational profiles (red line).