Mass analyzed threshold ionization spectroscopy of o-fluorophenol and o-methoxyphenol cations and influence of the nature and relative location of substituents

The mass analyzed threshold ionization spectra of o-fluorophenol and o-methoxyphenol were recorded via many of their respective vibronic states. The adiabatic ionization energies (IEs) of o-fluorophenol and o-methoxyphenol are determined to be 70,006 and 63,995 cm−1, respectively. Comparing these values with those in the literature, one finds that the IE follows the order: para < ortho < meta for fluorophenols, fluoroanilines, methylanilines, and methoxyphenols. The active vibrations of the o-fluorophenol and o-methoxyphenol cations include the C-OH and C-F bending mode 9b and in-plane ring deformation vibrations 6a, 1, and 12. The frequencies of each of these modes are slightly different for the two cations. The present studies show that the nature and relative location of substituents on the ring can influence the IE and molecular vibration.