Terahertz Vibration−Rotation−Tunneling Spectroscopy of the Ammonia Dimer. II. A−E States of an Out-of-Plane Vibration and an In-Plane Vibration

Abstract

Terahertz vibration-rotation-tunneling transitions have been measured between ca. 78.5 and 91.9 cm -1 , and assigned to A-E (ortho-para) combinations of NH 3 monomer states. The spectrum is complicated by inversion splittings that correlate to E symmetry monomer rovibronic states. Twenty progressions have been assigned to six excited states involving an out-of-plane vibration and an in-plane intermolecular vibration. The quality of the fit was affected by strong Coriolis interactions among these states and possibly an additional K ) 2 state that was not explicitly observed in the data.

Deconstructing Vibrational Motions on the Potential Energy Surfaces of Hydrogen-Bonded Complexes

“…8 The hydrogen bond of the ammonia dimer is considerably bent from the ideal linear configuration (unlike that of the water dimer), 9 which has led to extensive studies of this particular intermolecular interaction. [8][9][10][11][12][13][14][15][16][17][18][19] It is now evident from both experimental and theoretical studies that the intermolecular PES of the ammonia dimer is indeed extremely flat. [16][17][18] To disentangle the contributions of vibrational motions on the PES, one needs to achieve well-resolved vibrational spectra.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19] It is now evident from both experimental and theoretical studies that the intermolecular PES of the ammonia dimer is indeed extremely flat. [16][17][18] To disentangle the contributions of vibrational motions on the PES, one needs to achieve well-resolved vibrational spectra. IR spectra of ammonia dimers were measured previously, 20,21 but the assignment of the structures and vibrational motions was not definitive due to the nominally low signal level and lack of high-level theoretical analysis.…”

Terahertz vibration-rotation-tunneling spectroscopy of the propane–water dimer: The ortho-state of a 20 cm−1 torsion

“…A possible explanation for this is the large amplitude motions of the water molecule. As observed for the ammonia dimer [21][22][23] and argon-water dimer [24], a large amplitude motion of similar timescale can exhibit significant mixing with A axis rotation and other internal motions. The proposed structure for the propane-water dimer is shown in Figure 2.…”