Accurate electron affinity of Ti and fine structures of its anions

The high-resolution photoelectron energy spectra of atomic titanium and its hydride anions were obtained on a slow-electron velocity-map imaging spectrometer equipped with a cold ion trap. The cold ion trap employed in the present measurement was found to be very helpful for reducing the interference from the titanium hydride anions. The electron affinity of Ti was determined to be 609.29(34) cm^-1 or 75.54(4) meV. The accuracy was improved by a factor of 350 compared with the previous result. The fine structures of Ti^- were clearly resolved: 70.0(12)(⁴F_5/2), 165.2(15)(⁴F_7/2), and 285.2(15) cm^-1 (⁴F_9/2) above its ground state ⁴F_3/2. Moreover, the measured electron affinity and vibrational frequency of TiH can be reproduced well using the high level calculations.