Infrared photodissociation spectroscopy of protonated ammonia cluster ions, NH4+(NH3)n (n=5–8), by using infrared free electron laser

Abstract

Infrared photodissociation action spectra of protonated ammonia cluster ions, NH(4) (+)(NH(3))(n) (n=5-8), were measured in the range of 1020-1210 cm(-1) by using a tunable infrared free electron laser. Analyses by the density functional theory (DFT) show that the spectral features observed can be assigned to the nu(2) vibrational mode of the NH(3) molecules in NH(4) (+)(NH(3))(n). Size dependence of the spectra supports structural models obtained by the DFT calculations, in which the NH(4) (+) ion is solvated by the four nearest-neighbor NH(3) molecules. For NH(4) (+)(NH(3))(5), the spectrum between 1000 and 1700 cm(-1) was measured. The nu(4) bands of the NH(3) molecules and the NH(4) (+) ion were found in the range of 1420-1700 cm(-1).

Gas‐Phase Infrared Spectroscopy and Multidimensional Quantum Calculations of the Protonated Ammonia Dimer N2H7+

“…[14] For larger systems (n = 3-9), photodissociation spectra at longer wavelengths have been reported using a line-tunable CO 2 laser [15] or a free electron laser. [16,17] These studies have shown that while the n > 1 clusters prefer to form an ammonium ion solvated by ammonia molecules, the protonated ammonia dimer is unique in that it adopts a D 3d equilibrium geometry, with the excess proton shared equally between two ammonia molecules. Computationally, the structure and spectroscopic characteristics of (NH 4 + )(NH 3 ) n clusters have been studied mainly within the harmonic approximation (see references [18,19] and references therein) or using an effective onedimensional quantum model [20] of the N···H + ···N sharedproton stretching vibration in N 2 H 7 + .…”

Investigations of Scope and Mechanism of Nickel‐Catalyzed Transformations of Glycosyl Trichloroacetimidates to Glycosyl Trichloroacetamides and Subsequent, Atom‐Economical, One‐Step Conversion to α‐Urea‐Glycosides

“…Gas‐phase IR spectroscopy of N 2 H 7 + , the Zundel cation analogue in protonated ammonia clusters (NH 4 + )(NH 3 ) n , has to date been restricted to the range above 2600 cm −1 14. For larger systems ( n =3–9), photodissociation spectra at longer wavelengths have been reported using a line‐tunable CO 2 laser15 or a free electron laser 16. 17 These studies have shown that while the n >1 clusters prefer to form an ammonium ion solvated by ammonia molecules, the protonated ammonia dimer is unique in that it adopts a D 3 d equilibrium geometry, with the excess proton shared equally between two ammonia molecules.…”

H/D isotope effects on the geometry and infrared spectrum of the protonated ammonia dimer

“…This study in particular suggested that in the smallest cluster, N 2 H þ 7 , the proton is equally shared between the two ammonia molecules, i.e., midway between the two N atoms. Subsequent investigations of clusters ranging from n ¼ 3 to 8 payed special attention to the spectral signatures of the solvation shell structure [13][14][15]. Very recently the gas phase IR spectrum of N 2 H þ 7 in the region below 1000 cm À1 has been reported [16,17] and the frequency of the fundamental asymmetric stretching vibration of the shared proton was found to be as small as 374 cm À1 .…”