Fermi resonance interaction in hetero-dimer and trimer ions containing aniline+

Abstract

Vibrational spectra of hetero-dimer and trimer ions containing aniline + are measured by infrared photodissociation spectroscopy. For the dimer ions, the NH 2 bending overto ne band gains its intensity through Fermi resonance interaction with the hydrogen-bonded NH stretching fundamental. Unperturbed frequencies of the NH 2 bending overtone are ca lculated to be in the range of 3255-3276 cm-1 , suggesting that the frequency is almost inta ct upon cluster formation. For the trimer ions, Fermi resonance interaction occurs mainly between the NH 2 bending overtone and the stretching fundamental of the NH oscillator in volved in the stronger hydrogen bond.

Conformation of Benzo-12-Crown-4 Complexes with Ammonium Ions Investigated by Cold Gas-Phase Spectroscopy

“…This result is probably because the intermolecular interaction with B12C4 is weaker for EtNH 3 + than for MeNH 3 + ; the frequency of the hydrogen-bonded NH stretching vibration is higher and closer to that of the NH 2 bending overtone for the EtNH 3 + complex, giving more intensity to the overtone. 49 This trend in the intermolecular interaction for the EtNH 3 + and MeNH 3 + complexes is consistent with the position of the origin band in the UVPD spectra. The EtNH 3 + complex has an origin band at 36 466 cm −1 (Figure 1d and Table 1), which is 28 cm −1 lower than that of the MeNH 3 + complex (i.e., 36 494 cm −1 ) (Figure 1c and Table 1).…”

“…These bands are assignable to the overtone of the NH 2 bending vibration. 49 The intensity of these overtone bands relative to the free and hydrogen-bonded NH stretch is stronger for the EtNH 3 + complex than for the MeNH 3 + complex (Figure 3a). This result is probably because the intermolecular interaction with B12C4 is weaker for EtNH 3 + than for MeNH 3 + ; the frequency of the hydrogen-bonded NH stretching vibration is higher and closer to that of the NH 2 bending overtone for the EtNH 3 + complex, giving more intensity to the overtone.…”

“…This band could be due to the overtone of the NH 2 bending vibration gaining intensity through the Fermi resonance with the hydrogen-bonded NH stretching vibration. 49 The quantum chemical calculations of the B12C4 complexes provided several stable conformers within the relative total energy of 5 kJ mol −1 ; the stable isomers are displayed in Figures S2−S9. The ammonium complexes' conformation found in the experiments cannot be determined using only the calculated total energy.…”

“…Strong and broad bands assignable to the hydrogen-bonded NH stretch were observed at ∼2975 cm −1 , accompanied by an overtone of the NH 2 bending vibration at ∼3090 cm −1 , in both spectra. 49 In the next section, the conformation of the B12C4 complex is determined based on the UVPD and IR−UV results with quantum chemical calculations.…”

Anharmonic coupling between fundamental modes in tetramethylurea

“…11,12 And Fermi resonance does not really produce additional bands in the spectrum. Normally, Fermi resonance comes into being between fundamental and overtone or combination modes; [11][12][13][14][15][16] it has never been observed between two fundamental modes, as a result of not being satisfied in the symmetry and energy factors between the two non-degeneracy fundamental modes.…”