Relaxation processes of molecules on a solution surface studied by the two-color pump-probe ionization technique

A propanol (PrOH) solution of aniline (AN) was introduced into a vacuum chamber as a continuous liquid flow (liquid beam) and was irradiated with pump and probe laser beams having wavelengths of 266 and 500-600 nm, respectively. Ions produced by multiphoton absorption and ejected from the liquid beam surface were analyzed by a time-of-flight mass spectrometer, The mass spectra show that AN(+)(PrOH)(n) and H(+)(PrOH)(n) are produced. The AN(+)(PrOH)(n) and H(+)(PrOH)(n) intensities were measured as a function of the delay time between the pump and the probe lasers, The lifetime for relaxation of an excited aniline molecule on the liquid surface was obtained to be 7.8 ns from the dependence of the AN(+)(PrOH)(n) intensity on the delay time. In comparison with the lifetimes of an isolated aniline molecule in the gas phase and an aniline molecule in bulk solution, it is concluded that the aniline molecule does not strongly interact with ifs surrounding propanol molecules on the surface. Variation of the H(+)(PrOH)(n) intensity with the delay time indicates that H(+) produced by dissociative ionization of an aniline molecule is ejected with several propanol molecules as H(+)(PrOH)(n).