IR-INDUCED CHANGE IN THE MICROSCOPIC HYDRATION STRUCTURES OF PHENOL CATIONS TRAPPED IN THE COLD ION TRAP

Gas-phase hydrated clusters are treated as a microscopic model of hydration networks. Recently, we have revealed the temperature-dependence of hydration structures of hydrated phenol cation, [PhOH(H$_2$O)$_5$]$^+.$\footnote{H.~Ishikawa, I.~Kurusu, R.~Yagi, R.~Kato, Y.~Kasahara, \textit{J. Phys. Chem. Lett.} \textbf{8}, 2641 (2017).} In the cold condition (30 K), only an isomer having a ring-with-tail type hydration motif ($Rt$ isomer) exists, whereas chain-like isomers ($Ch$ isomer) are dominant in the hot condition (150 K). Isomerizations among the isomers having distinct hydration motifs can be related to structural fluctuations in the bulk systems. Thus, we have investigated the isomerization of the hydrated phenol cation trapped in the cold trap. In the last symposium, we reported the observation of the isomerization from the $Rt$ to the $Ch$ isomers. However, the quality of the spectra was not good enough. To improve the signal to noize ratio of the spectra, we introduced an octopole ion trap instead of the 22-pole ion trap, since an spatial overlap between the ions and the laser beam is expected to be better. In the present paper, we will report the progress of our study involving the time profile of the isomerization induced by the IR excitation