Infrared photodissociation spectroscopy of (n = 3 and 4) by using free electron laser

Photodissociation spectra of NH 4 + ( NH 3 ) n were measured for n = 3 and 4 in the range of 1070–1680 cm−1 by using an infrared free electron laser. Three vibrational bands observed for each species are assigned to the intramolecular vibrational modes: the ν2 and ν4 modes of NH3 and the ν4 mode of NH 4 + . When the first solvation shell is completed at n = 4, the ν2(NH3) and ν 4 ( NH 4 + ) wavenumbers are found to be higher by 182 and 36 cm−1, respectively, than those in free molecules, whereas the ν4(NH3) wavenumber is lower by 29 cm−1.