71st ISMS UV Photodissociation Spectroscopy of Temperature-Controlled Hydrated Phenol Cluster Cation Itaru KURUSU, Reona YAGI, Yasutoshi KASAHARA, Haruki ISHIKAWA, (Kitasato Univ.) harukisc@kitasato-u.ac.jp

Microscopic hydration in molecular clusters Owing to the development of the IR spectroscopic techniques, hydration structures of various clusters have been revealed . The next stage for the investigation on the microscopic hydration is to understand the temperature effect. n = 1 n = 1 n = 4 n = 2 n = 2 n = 3 n = 5 n = 4 n = 3 n = 5

Temperature effects on hydration structures Low temperature High temperature Isomerization fluctuation The study of temperature effects on hydration structures in the gas phase should provide us with information about structural fluctuations in the bulk.

Spectroscopy of Temperature-controlled hydrated clusters Temperature effects on microscopic hydration Rare gas tagging Cryogenically-cooled ion trap Present study Temperature-variable 22-pole ion trap apparatus UV photodissociation spectroscopy of hydrated phenol cation; [PhOH(H2O)n]+ n = 5 Spectroscopic information is available.

Temperature-variable 22-pole ion trap apparatus Ref. Fujihara, et al. J. Phys. Chem. A 113, 8169 (2009). Ishikawa, et al. Chem. Phys. Lett. 514 , 234 (2011). 1st Q-mass filter 2nd Q-mass analyzer Photodissociation laser Octopole ion guide 22-pole ion trap (30 – 300 K) Ionization laser Pulsed nozzle

UV PD spectrum of [PhOH(H2O)5]+ TTrap = 20 K Absorption of phenoxy radical Vibronic bands How many isomers?

Assignment of the bands of [PhOH(H2O)5]+ UV PD spectrum of [PhOH-TMA]+ Ref. N. Mikami, Bull. Chem. Soc. Jpn. 68, 683 (1995). Same band pattern as [PhOH-TMA]+ There seems to be one isomer in our condition.

Temperature dependence of the PD spectra of [PhOH(H2O)5]+ TTrap = 20 K Same pattern TTrap = 20 K vs. 50 K Additional band pattern appears at the high energy side. At least two isomers or two groups of isomers exist in our observation. Relative populations among these isomers depend on the temperature. 50 K 100 K 150 K w/o trap

DFT calculation for [PhOH(H2O)5]+ Gaussian 09 wB97X-D/6-311++G(d,p) Cyclic with tail 140 cm-1 95 cm-1 Bi-cyclic DE0 = 0 cm-1 112 cm-1 149 cm-1 Linear DE0 = 400 cm-1 598 cm-1 649 cm-1

Temperature dependence Relative population among the H-bond motifs Entropic effect of the flexibility of the H-bond network Similar dependence is reported for H+(MeOH)n DE0 = 0 cm-1 Cyclic with tail Linear DE0 = 400 cm-1 Ref. Chem. Phys. Phys. Chem. 17, 22042 (2015). Bi-cyclic DE0 = 95 cm-1

Possible assignments Qualitative agreement! Relative population among the H-bond motifs TTrap = 20 K Cyclic with tail 50 K 100 K Linear 150 K w/o trap Qualitative agreement!

Summary PD spectroscopy of temperature-controlled [PhOH(H2O)5]+ is carried out. At least two isomers are identified. Relative population among the isomers is examined based on the DFT calculation. The spectral change observed is qualitatively considered. Future Extension of PD spectroscopy 0-0 region, the other sized clusters, IR Detailed discussion based on both the measurements and calculations Dynamical properties