Autoionization-detected infrared spectroscopy of intramolecular hydrogen bonds in aromatic cations. I. Principle and application to fluorophenol and methoxyphenol

Abstract

A new infrared spectroscopic technique for jet-cooled molecular cations is applied to observe intramolecular hydrogen bonds in substituted phenol ions. Vibrational transitions of an ion core of high Rydberg states are measured by detecting molecular ions prepared through vibrational autoionization. The observed infrared spectra practically provide vibrational frequencies of the corresponding bare molecular ion. The OH stretching vibrations of ortho-, meta-, and para-isomers of fluorophenol and methoxyphenol cations are observed. The OH stretching vibrational frequency of the ortho-isomer shows a characteristic redshift due to the intramolecular hydrogen bond. The redshift increases with ionization, indicating a significant enhancement of the intramolecular hydrogen bond strength.

Mass analyzed threshold ionization detected infrared spectroscopy: isomerization activity of the phenol–Ar cluster near the ionization threshold

“…This frequency agrees well with n OH of bare PhOH + obtained by ADIR spectroscopy 29,30 and can be assigned to n p OH of the p-bound PhOH + -Ar ion core. The width of the n p OH band (B5 cm À1 ) is, however, smaller than that of the n OH band obtained from ADIR spectroscopy (B20 cm À1 ) 29,30 even though the depletion is mostly saturated. This difference has been attributed to electron detachment dynamics in ADIR spectroscopy.…”

Spectroscopic Investigation of cis-2,4-Difluorophenol Cation by Mass-analyzed Threshold Ionization Spectroscopy

“…13 With help from theoretical calculations, they proposed that that presence of an intramolecular OH F bonding preferentially stabilizes the cis conformer of 24DFP, as that observed in 2-fluorophenol. 8,12,14 A similar observation has been reported for 2-fluorophenol 14 and 2-chlorophenol. 35 We have performed the Becke three-parameter with the PW91 correlation functional (B3PW91) calculations with the 6-311++G(d,p) basis set to investigate the stable rotamers Figure 4.…”

“…13 They proposed that the cis and trans rotamers of 24DFP coexist and possess the intramolecular OH F bonding, as that observed in 2-fluorophenol. 8,12,14 In addition, the cis form is more abundant than the trans form. Anbarasan and coworkers recorded the infrared and Raman spectra of 24DFP in the condensed phase and reported the active vibrations of this molecule in the S 0 state.…”

“…2-Fluorophenol is regarded as one of the classic example of intramolecular hydrogen-bonding systems which have been the subject of various studies. [6][7][8][9][10][11][12] Chakrabarti et al applied radiofrequency-microwave double resonance (RFMWDR) and conventional microwave spectroscopic techniques to record the microwave rotational spectra of gas-phase 2,4-difluorophenol (24DFP) in the ground S 0 state. 13 They proposed that the cis and trans rotamers of 24DFP coexist and possess the intramolecular OH F bonding, as that observed in 2-fluorophenol.…”

“…[1][2][3] Many fluorinated benzene derivatives, [4][5][6][7][8][9][10][11][12][13][14][15][16] are extensively studied by various spectroscopic methods. 2-Fluorophenol is regarded as one of the classic example of intramolecular hydrogen-bonding systems which have been the subject of various studies.…”