DOI: 10.5061/dryad.547d7wmkw
title: Data from: Microcanonical kinetics of water-mediated, long range proton transfer in microhydrated 4-aminobenzoic acid

description: We report the microcanonical kinetics of vibrationally-induced,
 water-network-mediated proton transfer across the neutral acid scaffold,
 4-aminobenzoic acid (4ABA), in isolated cationic clusters. Protonation of
 neutral 4ABA occurs at the acid (O-protomer) and amine (N-protomer)
 functionalities of 4ABA, yielding two distinct species whose relative
 energies depend on the degree of hydration. Here we measure the rates of
 intramolecular proton transfer in 4ABAH+·(H2O)6 ions upon
 protomer-selective vibrational excitation of initially cold (6K) cluster
 ions isolated in a cryogenic ion trap. Interconversion rates are observed
 on the microsecond time scale. These results quantify the kinetics of
 proton transfers in the context of a closed, finite system at well-defined
 internal energies and therefore provide unprecedented experimental
 benchmarks for theoretical efforts that are being developed to treat
 relatively slow, highly cooperative solvent-mediated chemical processes.
description: # Data from: Microcanonical kinetics of water-mediated, long range proton
 transfer in microhydrated 4-aminobenzoic acid Dataset DOI:
 [10.5061/dryad.547d7wmkw](10.5061/dryad.547d7wmkw) ## Description of the
 data and file structure All raw data — including IR, UV, mass spectra, and
 kinetics plots — presented in the figures have been compiled into an Excel
 file(data_July10.xlsx). Each dataset is placed on a separate sheet, named
 according to its corresponding figure. The contents of each sheet are
 described in detail below: Figure 1: Contains the UV photofragmentation
 spectra of the N- and O-protomers shown in Figure 1A of the manuscript.
 Columns A–B: N-protomer data — wavelength (nm) and intensity. Columns E–F:
 O-protomer data — wavelength (nm) and intensity. Data are organized in
 paired columns for each protomer. Figure 2: Contains IRMPD spectra for the
 N- and O-protomers corresponding to Figures 2A and 2B.\ Columns A–B:
 O-protomer spectrum (wavenumber in cm⁻¹, intensity). Columns D–E:
 N-protomer spectrum (wavenumber in cm⁻¹, intensity). The first row
 indicates figure panel assignments. Figure 3a: Time-resolved UV spectra of
 O·(H₂O)₆ after IR excitation (Figure 3A). Three spectra: “no IR pump”, “1
 μs delay”, and “20 ns delay”. Each spectrum stored in a
 wavelength–intensity column pair. Figure 3b: Kinetics trace corresponding
 to the decay of O-protomer signal at 310 nm after IR excitation. Columns:
 delay (ns), delay (μs), relative population change, and standard error.
 Single-exponential fit reported in the manuscript. Figure 4a:
 Time-resolved UV spectra of O·(H₂O)₆ following N-protomer excitation
 (Figure 4A).\ Spectra for “no IR pump”, “1 μs delay”, and “6 μs delay”.
 Stored in paired wavelength–intensity columns. Figure 4b: Kinetics trace
 for the O-protomer signal at 310 nm after N-protomer excitation. Columns:
 delay (ns), delay (μs), relative population change, and error. Figure S1:
 Mass spectra corresponding to Figure S1. Multiple experimental stages:
 before mass isolation, after mass isolation, after IR pump, and after UV
 probe. Each spectrum stored in m/z–intensity column pairs. The first row
 indicates figure panel assignments. Figure S4: UV spectra for N- and
 O-protomers with varying hydration levels, corresponding to Figure S4.
 Multiple spectra (labeled A–J, in 1st row) each in wavelength–intensity
 column pairs. Figure S5: Full-range UV spectrum of O·(H₂O)₆. Columns:
 wavelength (nm) and intensity. Figure S6: IRMPD spectra with and without
 O-protomer UV bleach, and difference spectrum. Columns: wavenumber (cm⁻¹),
 UV bleach off, UV bleach on, bleach-on minus bleach-off. Figure S7:
 Contains IRMPD spectra used to extract the N·(H₂O)₆ spectrum from a mixed
 population of N- and O-protomers. Panel A (Columns A–B): Mixed-protomer
 IRMPD spectrum — wavenumber (cm⁻¹) and intensity. Panel B (Columns F–G):
 O-protomer spectrum obtained via selective UV bleaching (296 nm) —
 wavenumber (cm⁻¹) and intensity. Panel C (Columns J–K): N-protomer
 spectrum derived by subtracting the O-protomer contribution from the mixed
 spectrum — wavenumber (cm⁻¹) and intensity. Figure S8: Contains IR pump–IR
 probe difference spectra demonstrating bidirectional proton transfer
 between O·(H₂O)₆ and N·(H₂O)₆. Panel A (Columns A–D): IRMPD spectra with
 the IR pump laser off, IR pump laser on (O-protomer excitation at 3290
 cm⁻¹), and the corresponding difference spectrum (pump on – pump off),
 plotted as a function of wavenumber (cm⁻¹). Panel B (Columns G–H):
 Expanded view of the difference spectrum from Panel A (pump on – pump off)
 to highlight spectral changes upon O→N conversion. Panel C (Columns K–L):
 Difference spectrum obtained after exciting the N-protomer, showing
 depletion of N features and appearance of O-protomer bands (N→O
 conversion). Figure S9: Contains D₂-tagged IR spectra in the fingerprint
 region for mixed and O-specific protomer populations. Panel A (Columns
 A–B): D₂-tagged IR spectrum of the mixed 4ABAH⁺·(H₂O)₆ population —
 wavenumber (cm⁻¹) and intensity. Panel B (Columns E–F): D₂-tagged IR
 spectrum of the O-protomer obtained by UV bleach modulation at 296 nm —
 wavenumber (cm⁻¹) and intensity. Figure S10: Kinetics trace showing the
 growth of the O·(H₂O)₆ population following selective excitation of
 N·(H₂O)₆ at 3645 cm⁻¹. Columns A–D: Delay time in nanoseconds (ns) and
 microseconds (μs), relative population change, and standard error. Figure
 S11: Kinetics traces for N→O proton transfer probed at different UV
 wavelengths. Columns A–D: Delay time in nanoseconds (ns) and microseconds
 (μs), relative population change (315 nm probe), and standard error.
 Figure S12: Calculated internal vibrational energies for N·(H₂O)₆ and
 O·(H₂O)₆ as a function of temperature. Columns A–C: Temperature (K),
 internal energy for N-protomer (cm⁻¹), internal energy for O-protomer
 (cm⁻¹).