Mass analyzed threshold ionization spectroscopy of p-ethylaniline cation: alkyl chain effects on ionization and molecular vibration

We report the mass analyzed threshold ionization (MATI) spectra of p-ethylaniline recorded via the 00 vibrationless and the 6a1,11,I2 and 121 vibrational levels of S1 state. The adiabatic ionization energies (IE) of this molecule is determined to be 59 959±5 cm−1 and most of the active vibrations of its cation are related to the in-plane ring vibrations. Comparison among the present results and those of aniline, p-methylaniline, and p-propylaniline shows that the IE decreases as the length of the alkyl chain increases. In addition, the long chain effect on the frequencies of the observed in-plane ring vibrations is insignificant. These experimental findings are supported by ab initio and density functional theory (DFT) calculations.