Zero Kinetic Energy Spectroscopy of AlNH₃ Complex

Pulsed field ionization-zero kinetic energy photoelectron spectrum of the jet-cooled aluminum-ammonia complex, AlNH₃, has been observed for the first time. The spectrum shows vibronic transitions from two spin-orbit levels of the neutral ground state, which allows the measurements of the following spectroscopic constants: ionization potential, 39746 cm^-1; spin-orbit splitting, 58 cm^-1; intermolecular stretching vibrational frequencies, omega₃⁺ = 339 cm^-1, omega₃⁺ chi₃⁺ = 3.1 cm^-1, and omega₃ = 227 cm^-1; intermolecular bending frequency, upsilon₆⁺ = 557 cm^-1. The observation of the spin-orbit splitting confirms that the ground state of the neutral complex is the ²E state.