Accurate ionization potentials of phenol and phenol-(H2O) from the electric field dependence of the pump–probe photoionization threshold

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Abstract
The adiabatic ionization potentials of phenol and phenol‐(H2O) have been obtained from pump–probe photoionization threshold measurements in a supersonic molecular beam time‐of‐flight mass spectrometer. The observed photoionization thresholds were found to vary linearly with the square root of the ion‐extraction electric field over fields ranging from 27 to 500 V/cm. Extrapolations to zero field yields IPs of 68 623±10 cm−1 for phenol and 64 035±10 cm−1 for phenol‐(H2O). Thus, hydrogen bonding to one water molecule lowers the ionization potential of phenol by 4590±15 cm−1. The advantages of this technique of measuring ionization potentials are discussed.