Itaru KURUSU, Reona YAGI, Yasutoshi KASAHARA, Haruki ISHIKAWA Department of Chemistry, School of Science, Kitasato University ULTRAVIOLET AND INFRARED PHOTODISSOCIATION SPECTROSCOPY OF HYDRATED ANILINIUM ION

Temperature effect on the hydrated structure We have been carrying out laser spectroscopy on the temperature-controlled hydrated phenol cation. To gain wide insights into the microscopic hydration, anilinium ion (AnH + ) is chosen as a solute. Introduction

Hydrated anilinium ion: AnH + (H 2 O) ｎ Different hydration structures are expected. Difference in electronic configuration H 2 O molecules surround AnH + H 2 O molecules get together around OH group

Isomer of anilinium ion: Carbenium ion  E = 1823 cm −1 The existence of carbenium ion in the gas phase is investigated by IR spectroscopy. M05-2X/6-31++G(d,p)  E = 0.0 cm −1  E = 298 cm −1 p-carbenium ion o-carbenium ion

IR spectrum of AnH + -N 2 - A 1, A 2, A 3 and D 1 bands : anilinium ion - B 1 and B 2 bands : carbenium ion Both of the anilinium and the carbenium ions exist. Ref. O. Dopfer, et al., J. Phys. Chem. A 110, (2006).

Previous reports on AnH + There is no spectroscopic report on the AnH + (H 2 O) n. Collision induced dissociation ( CID ) experiment on the AnH + -H 2 O - Binding energy: 59.8 kJ/mol Ref. P. G. Wenthold, et al., J. Phys. Chem. A 117, 1166 (2013). Electronic spectrum of the AnH + in the gas phase Ref. C. Jouvet, et al., Phys. Chem. Chem. Phys. 16, 5252 (2014). Blue shifted by about 4200 cm -1 from that of the neutral aniline This work: UV and IR spectroscopy of the AnH + (H 2 O)

Sample solution ・・・ 0.5 mM aqueous solution of C 6 H 5 NH 2 ·HC ｌ with 0.5% of acetic acid 噴煙 Electrospray ionization (ESI) Ref. Spray tip (+HV) Generation of AnH + (H 2 O) n

Photodissociation spectroscopy Packets of clusters are generated by trapping using octopole ion guide. 22-pole ion trap is used as ion guide. PD spectra are measured by monitoring the photofragment, AnH +. UV or IR

UV PD spectrum of AnH + (H 2 O) ~ 950 cm -1 AnH + - The origin band is red shifted by 1863 cm -1. · · · The H-bond is strengthened in the excited state. - The band pattern is similar to that of the AnH +. · · · The structure of the AnH + is not so affected by the hydration. - Band shape is shaded to the lower frequency side. · · · Hot bands may contribute.

IR PD spectrum of AnH + (H 2 O) Free NH Sym. OH Anti-sym. OH

Computational results of AnH + (H 2 O)  E = 0.0 cm -1  E = 1603 cm -1  E = 3632 cm -1 Three structures exhibit distinct NH stretch band patterns. H-bonded NH str. Observed range M05-2X/6-31++G(d,p)  E = 0.0 cm −1  E = 298 cm −1 p-carbenium ion anilinium ion

NH ・・・ O bond distance ： Å Binding energy ： 68.9 kJ/mol (calc.) 59.8 kJ/mol (CID exp.) Ref. P. G. Wenthold, et al., J. Phys. Chem. A 117, 1166 (2013). Comparison of experimental and calculated IR spectrum

Conclusion UV and IR spectra of AnH + (H 2 O) are measured for the first time. Structure of the AnH + (H 2 O) is determined by the IR spectroscopy and the DFT calculation. UV and IR spectroscopy under the temperature- controlled condition Extension to the larger hydrated clusters Future work

Mass spectrum of AnH + (H 2 O) n We have succeeded in producing the n = 1 – 8 clusters.

AnH + H2OH2O 59.8 kJ/mol S0S0 S1S cm cm -1 AnH + ・ H 2 O 1863 cm -1 Increasing H-bond strength in the excited state

Spectroscopic study of molecular cluster in the gas phase ・ Molecular cluster in gas phase ・・・ Microscopic model of condensed phase ・ Various measurement selecting number of solvent molecules is possible. ・ Determination of the solvated structures for various molecular cluster in gas phase by the development of IR spectroscopy Condensed phase molecular cluster in the gas phase

NH ・・・ O bond distance ： Å Binding energy ： 68.9 kJ/mol (calc.) 59.8 kJ/mol (CID exp.) Ref. P. G. Wenthold, et al., J. Phys. Chem. A 117, 1166 (2013). Comparison of experimental and calculated IR spectrum OH anti sym. str. + H 2 O internal rotation

Future work Temperature-variable 22-pole ion trap - UV and IR spectroscopic measurement under temperature-controlled condition