PROBING THE STRUCTURES OF NEUTRAL B11 AND B12 USING HIGH-RESOLUTION PHOTOELECTRON IMAGING OF B11− AND B12−

We report high-resolution photoelectron imaging of B$_{11}$$^-$ and B$_{12}$$^-$ at 354.7 and 532.0 nm, respectively, resolving several low-frequency vibrational modes for neutral B$_{11}$ and B$_{12}$. The vibrational information is highly valuable to verify the structures of the neutral clusters. Several isomers are considered, and vibrational frequencies are calculated for B$_{11}$ and B$_{12}$ using density functional theory. Comparisons between the experimental and calculated vibrational frequencies prove that the B$_{11}$ neutral and anion both possess a perfectly planar C$_{2v}$ structure. The B$_{12}$$^-$ anion is quasi-planar with C$_s$ symmetry, while the experiment confirms that neutral B$_{12}$ possesses C$_{3v}$ symmetry. The high-resolution photoelectron spectra also allow the electron affinities of B$_{11}$ and B$_{12}$ to be measured more accurately as 3.401 and 2.221 eV, respectively. It is shown that high-resolution photoelectron imaging can be an effective method to determine structures of small neutral boron clusters, complementary to infrared spectroscopy