The cyclic ground state structure of the HF trimer revealed by far infrared jet-cooled Fourier transform spectroscopy

Abstract

The rovibrationally resolved Fourier transform (FT) far infrared (FIR) spectra of two intermolecular librations of (HF)3, namely the in-plane ν6 and out-of-plane ν4 bending fundamentals centered, respectively, at about 494 cm(-1) and 602 cm(-1), have been recorded for the first time under jet-cooled conditions using the supersonic jet of the Jet-AILES apparatus. The simultaneous rotational analysis of 245 infrared transitions belonging to both bands enabled us to determine the ground state (GS), ν6 and ν4 rotational and centrifugal distortion constants. These results provided definite experimental answers to the structure of such a weakly bound trimer: firstly the vibrationally averaged planarity of cyclic (HF)3, also supported by the very small value of the inertia defect obtained in the GS, secondly the slight weakening of the hydrogen bond in the intermolecular excited states evidenced from the center of mass separations of the HF constituents determined in the ground, ν6 = 1 and ν4 = 1 states of (HF)3 as well as the decrease of the fitted rotational constants upon excitation. Finally, lower bounds of about 2 ns on ν6 and ν4 state lifetimes could be derived from the deconvolution of experimental linewidths. Such long lifetimes highlight the interest in probing low frequency intermolecular motions of molecular complexes to get rid of constraints related to the vibrational dynamics of coupled anharmonic vibrations at higher energy, resulting in loss of rotational information.

Competition between inter- and intra-molecular hydrogen bonding: An infrared spectroscopic study of jet-cooled amino-ethanol and its dimer

“…When replacing helium by argon, AE complexation is expected as evidenced in previous hydrogen bonded studies. 28 At low AE concentration ( Figure 1(b)), two additional features, broader than that of the monomer (3567.8 cm 1 ), appear at lower frequencies. They consist of an intense band at about 3304 cm 1 assigned to the dimer and a weaker one at 3388 cm 1 .…”

“…The procedure consisting of applying anharmonicity corrections calculated at the MP2 or DFT level to the CCSD(T)-F12 frequencies led to an excellent agreement between theory and experiment for floppy molecules as well as H-bonded systems. 28,35 Due to computational cost, a different procedure was followed for the dimer. The harmonic frequencies of the dimer were calculated at the MP2/AVTZ level and scaled by a mode-specific scaling factor, which takes into account the anharmonicity pattern specific to each vibration mode.…”

“…We revisit here the vibrational spectroscopy of AE and its dimer in the hydride stretch, mid infrared (MIR), and far infrared (FIR) regions, by means of the Jet-AILES apparatus, installed on the infrared beamline AILES at the synchrotron facility SOLEIL. [26][27][28] This experimental setup combines a continuous supersonic expansion with a pumping capacity adapted to high molecular flows and a high resolution Fourier Transform IR (FTIR) spectrometer. It enables probing the vibrational spectroscopy of gaseous and sublimated vapors of initially liquid or solid samples controlled in flow and temperature, over the whole IR range.…”

Overtone spectroscopy of molecular complexes containing small polyatomic molecules

“…Impressive developments around this approach are still on their way, in particular by Georges [145], Asselin et al [146], and Suhm [147,148], and their co-workers. Some of these works address van der Waals species [149,150].…”

O paradigma da estrutura do doador de próton na formação de ligações de hidrogênio: complexo C2H2∙∙∙6(HF)

“…Durante certo tempo foi debatido a estrutura do ácido fluorídrico trimolecular na forma de cadeia. 46 Muito recente, entretanto, Asselin et al 47 obtiveram, através da espectroscopia rotovibracional de infravermelho, que a real estrutura do trímero do ácido fluorídrico apresenta uma configuração cíclica. Não apenas no âmbito experimental, mas este resultado também foi confirmado através 48 Do ponto de vista das ligações de hidrogênio intramoleculares, que, em geral, apresentam distâncias em torno de 1,9000 Å, 49 inegavelmente que as ligações de hidrogênio no complexo C 2 H 2 •••6(HF) deveriam sim, provocar alterações mais contudentes na estrutura do receptor de próton.…”