Ground and low-lying excited states of phenoxy, 1-naphthoxy, and 2-naphthoxy radicals via anion photoelectron spectroscopy

Abstract

We present the slow electron velocity map imaging spectroscopy of cryogenically cooled phenoxide, 1-naphthoxide, and 2-naphthoxide anions. The results allow us to examine the ground state and the lowest energy excited state in the corresponding neutral radicals. Care was taken to minimize autodetachment signals in the photoelectron spectra, allowing for more straightforward comparisons with Franck-Condon analyses. The ground states of these three aromatic oxide radicals all have the unpaired electron residing in a π orbital delocalized throughout the molecule. The electron affinity of 1-naphthoxy is measured to be 2.290(2) eV, while that of 2-naphthoxy is measured to be 2.404(2) eV, both of which are higher than that of the smaller phenoxy molecule at 2.253(1) eV. The first excited states have the unpaired electron residing in a more localized σ orbital, yielding measured term energies for the state of 1.237(2) eV in 1-naphthoxy and 1.068(1) eV in 2-naphthoxy, while that of phenoxy is lower at 0.952(1) eV. The calculated Franck-Condon spectra generally showed good agreement with the experimental spectra, yielding assignments of the more active vibrations in each electronic state. Significant autodetachment signals arising from dipole bound states near the ground states of all three radicals were observed in our efforts to avoid them, and comparably less autodetachment signals were observed near the excited states. Besides this type of non-Franck-Condon intensities in the photoelectron spectra, we also observed minor features arising due to vibronic coupling in the ground states of all three radicals.

Autodetachment dynamics of 2-naphthoxide and implications for astrophysical anion abundance

“…2b), which was assigned to the principal Franck-Condon active mode for excitation of the S 1 (pp*) state (calculated n 32 (a 0 ) = 437 cm À1 ) through Franck-Condon-Herzberg-Teller simulations. 21 It is also worth noting that this vibrational structure is consistent with the principal Franck-Condon modes for direct photodetachment characterised by an earlier cryogenic photoelectron spectroscopy experiment, 22 involving n 32 (a 0 ) = 422 cm À1 (neutral), which is an in-plane CCC bending mode and has most displacement localised on the oxygen-containing benzyl ring. In the present photoelectron spectra, the vibrational structure over the prompt detachment band in the photoelectron spectra is presumably associated with prompt autodetachment through electron shake-off by the n 32 mode of the anion excited state.…”

“…Two recent investigations using cryogenic photoelectron and photodetachment techniques have reported near-threshold spectra of 2-Np À , and also identified dipole-bound states. 22,23 In this paper, we report a frequency-, angle-, and timeresolved photoelectron imaging study of 2-Np À thermalised to T E 300 K. The key questions that this study addresses are: (1) What is the lifetime of the S 1 (pp*) state when exciting at the 0-0 transition? (2) What are the decay dynamics of the excited state, and is there any internal conversion to recover the ground electronic state?…”

Influence of the N atom and its position on electron photodetachment of deprotonated indole and azaindole

“…In our case, the signal is essentially on a zero background and thus the sensitivity is orders of magnitude larger. Concerning DBSs, our resolution is similar to the resolution of SEVI 24 and is basically limited by the laser band width (~ 10cm -1 ). We used the DFT method implemented in the Gaussian 48 package with the CAM-B3LYP/augcc-pVDZ functional to calculate the adiabatic detachment energies (ADE), the dipole moments of the dehydrogenated radicals, and the vibrations of both the deprotonated anions and dehydrogenated radicals in order to calculate the difference in zero-point energy (ZPE) between the two species.…”

Photodetachment and photoreactions of substituted naphthalene anions in a tandem ion mobility spectrometer

“…The peaks above the detachment threshold at 19 600±10 and 20 020±20 cm −1 are associated with transitions to autodetaching, dipole-bound states (DBSs) as observed in slow electron velocity-map imaging spectroscopy of cryogenically cooled 2-naphtholate anions. 9 An even stronger peak below the detachment threshold at 19 180±10 cm −1 likely arises from excitation of the lowest-lying DBS, which does not autodetach, but which is detected in the drift tube environment because the excited 2-naphtholate anion transfers an electron directly to SF 6 in a collisional encounter. 37 The spacing between the first two DBS peaks is ≈420 cm −1 , presumably corresponding to an in-plane ring deformation vibrational mode.…”

“…To our knowledge, there is limited information on the intrinsic electronic absorptions of naphtholate anions in the gas phase, aside from recent photoelectron studies of 1-naphtholate and 2-naphtholate anions aimed mainly at understanding the properties of the 1-naphthoxy and 2-naphthoxy radicals, which focused on transitions to dipole-bound states near the electron detachment threshold. 9 The 6-hydroxy-2-naphthoic acid molecule possesses two deprotonation sites with the resulting deprotomers (Fig. 1(c) and (d)) expected to have quite different electronic properties.…”