Vibrational Feshbach resonances (VFRs) constitute fundamental doorway states governing electron attachment and vibrational autodetachment in molecular anions. However, their real-time dynamics has remained largely unexplored for valence-bound radical anions because the exceptionally small electron affinities of these species make direct time-resolved measurements experimentally challenging. Here we investigate the nitromethane anion (CH3NO2-), a prototypical valence-bound radical anion with an electron affinity of only ∼0.17 eV, using picosecond mid-infrared pump-probe photoelectron spectroscopy. Selective excitation of the symmetric CH3 stretching mode reveals a vibrational autodetachment lifetime of approximately 10 ps, determined directly using a depletion-based time-resolved photoelectron detection scheme. This time scale is orders of magnitude longer than expected for prompt vibrational electron emission, demonstrating that autodetachment is limited by intramolecular vibrational redistribution (IVR), which redistributes the initially localized vibrational energy before the system gains access to the electron-detachment continuum. Picosecond IR photoelectron spectra further reveal transient population transfer from the valence-bound anion to a dipole-bound state (DBS), providing direct evidence for reverse internal conversion induced by mode-selective vibrational excitation. These findings establish that VFRs in valence-bound radical anions are not merely precursors to electron emission but constitute dynamical gateways that partition excess-electron relaxation between autodetachment and reverse internal conversion. This mechanistic picture provides a unified framework for understanding electron-driven chemistry in weakly bound molecular anions.

Femtosecond time-resolved photoelectron spectroscopy combined with ab initio electronic structure and molecular dynamics calculations reveals the real-time structural and electronic evolution of sodium halide dimers, (NaCl)2 and (NaI)2, following vertical electron detachment from their corresponding anions. Both pseudo-linear dimer anions transform into rhombic neutral geometries upon electron detachment. Despite the weak binding of the excess electron, the dipole-bound state (DBS) of each anion temporarily traps the electron within a finite potential well, creating a tunneling barrier that governs autodetachment. The estimated lifetimes of DBS are ∼4 ps for (NaCl)2- and ∼40 ps for (NaI)2-, in excellent agreement with theoretical tunneling barrier heights of ∼50 and ∼100 meV, respectively. These results constitute the first direct experimental observation of tunneling autodetachment from a DBS and demonstrate how femtosecond structural relaxation of the neutral core drives quantum mechanical electron decay.

We report here direct experimental evidence of reverse internal conversion taking place in the excited nitrobenzene anion, revealed by photoelectron spectra acquired by electron detection at the much-delayed time with respect to the laser-anion interaction time along the time-of-flight. Especially, autodetached photoelectrons from the dipole bound states which are in quasi-equilibrium with vibrationally hot anions have been clearly observed concurrently with thermionic emission at the much-delayed time (up to 120 ns). Not only does this work confirm a proposed mechanism in previous reports, but also it demonstrates that the reverse internal conversion is robust across multiple electronically excited states of nitrobenzene anion, suggesting that it may play an important role in governing energy relaxation pathways of excited anionic states.

We reexamined hydrated electron motifs in water cluster anions using photoelectron and electronic absorption spectroscopies under identical ion source conditions. The structural motifs, previously characterized as four, are now established as five in the present work, thereby refining the framework of hydrated electron isomers. Time-resolved photoelectron spectroscopy revealed motif-dependent relaxation dynamics, with certain surface-bound species undergoing more efficient excited-state autodetachment than others. Extending the temporal probing window uncovered long-lived vibrationally excited ground-state anions (τ ∼ 340 ps), far exceeding prior expectations, while increasing cluster size enhanced internal conversion efficiency. These results closely align with theoretical predictions. More broadly, they demonstrate that excited-state dynamics are highly sensitive to local structure, giving rise to distinct relaxation pathways under different hydration environments. The structure-dynamics relationships established here provide a foundation for extending such studies to other hydrated species, advancing fundamental insight into electron solvation and relaxation in aqueous systems.

Low-energy electrons are a major source of radiation-induced damage to genetic material through attachment-induced bond rupture in DNA and RNA nucleobases. Here, we show that microsolvation fundamentally alters this process; even a single water molecule suppresses covalent bond rupture in electron-attached uracil. Using mass-selected hydrated uracil anions, we investigate fragmentation dynamics following photoexcitation over a wide energy range (0.5-5.5 eV). Rather than undergoing bond cleavage, electronically excited clusters relax via rapid internal conversion to a vibrationally hot ground state, followed by sequential water evaporation. Photofragment excitation spectroscopy reveals the electronic structures of individual hydrated uracil anions, while the observed solvent-loss patterns are quantitatively described by a stochastic evaporation model with an average water binding energy of similar to 0.4 eV, independent of cluster size. These results demonstrate that immediate hydration qualitatively redirects the relaxation pathways of electron-attached nucleobases, with important implications for understanding electron-driven chemistry in aqueous biological environments.

Low-energy electrons are a major source of radiation-induced damage to genetic material through attachment-induced bond rupture in DNA and RNA nucleobases. Here, we show that microsolvation fundamentally alters this process; even a single water molecule suppresses covalent bond rupture in electron-attached uracil. Using mass-selected hydrated uracil anions, we investigate fragmentation dynamics following photoexcitation over a wide energy range (0.5-5.5 eV). Rather than undergoing bond cleavage, electronically excited clusters relax via rapid internal conversion to a vibrationally hot ground state, followed by sequential water evaporation. Photofragment excitation spectroscopy reveals the electronic structures of individual hydrated uracil anions, while the observed solvent-loss patterns are quantitatively described by a stochastic evaporation model with an average water binding energy of ∼0.4 eV, independent of cluster size. These results demonstrate that immediate hydration qualitatively redirects the relaxation pathways of electron-attached nucleobases, with important implications for understanding electron-driven chemistry in aqueous biological environments.

We study the isomer-specific photoionisation and photofragmentation of 1,2-dibromoethene (DBE) under strong-field fs-laser irradiation in the gas phase complementing previous studies utilising ns- and ps-laser excitation. Our findings are compatible with a dissociative multiphoton-ionisation mechanism producing a variety of ionic photofragments. Using both Stark deflection and chemical separation of the two isomers, pronounced isomer-specific photofragmentation dynamics could be observed for different product channels. While for Br+ formation, the isomer specificity appears to originate from different photoexcitation efficiencies, for the C2H2Br+ channel it is more likely caused by differences in the coupling to the exit channel. By contrast, the formation of the C2H2+ photofragment does not seem to exhibit a pronounced isomeric dependence under the present conditions. The present work underlines the importance of isomeric effects in photochemistry even in small polyatomics like the present system as well as their pronounced dependence on the photoexcitation conditions.

Magic-sized clusters (MSCs) serve as well-defined model systems for investigating surface-related photophysical properties due to their atomically precise structures and monodispersity. However, indium phosphide (InP) MSCs suffer from an extremely low photoluminescence quantum yield (PLQY < 1%) due to persistent surface trap states, which not only limit their utility but also hinder a fundamental understanding of their surface chemistry and photophysics. Herein, we introduce a surface-engineering strategy that overcomes this limitation by enabling the controlled in situ HF generation via Friedel-Crafts acylation chemistry, achieving a record-high PLQY of 18.1%. Comprehensive surface analyses reveal that the enhancement arises from phosphonate ligand exchange and surface oxide removal. These modifications suppress charge carrier trapping and inhibit exciton thermal quenching at room temperature. Moreover, the altered surface environment leads to red-shifted and broadened emission, not due to size heterogeneity but rather to surface-dependent electronic states in InP MSCs. Density functional theory simulations support this mechanism by demonstrating a reduced trap state density near the valence band edge and revealing that the presence of isomeric surface configurations with slightly different energy levels is responsible for the observed spectral broadening. These findings provide a molecular-level understanding of surface-dependent excitonic behavior and establish an effective strategy for overcoming the intrinsic limitations of luminescence efficiency in InP MSCs.

Bifurcation dynamics into Herzberg type-I and type-II predissociation pathways at the conical intersection have been characterized in terms of their distinct reaction rates and energy-disposal dynamics from the picosecond time-resolved product state distributions measured at multiple S1/S2 vibronic states of thioanisole (C6H5SCH3). Electronic predissociation (type-I) occurs on a faster time scale and leads to the larger translational energies being released to the fragments (C6H5S• + •CH3) compared to the vibrational predissociation (type-II). While type-II dominates at the S1 zero-point level, the type-I quantum yield increases sharply near the S1/S2 conical intersection, which is consistent with the striking dynamic resonance observed for the reactive flux in the proximity of the conical intersection. Nonadiabatic product yield at the asymptotic limit was found to be enhanced predominantly through the type-I channel, suggesting that the quantum-mechanical nature of the reactive flux prepared near the first S1/S2 conical intersection is likely to be retained at the second S0/S2 conical intersection encountered in the later stage as there is little time to be altered during the ultrafast S-CH3 bond extension on the repulsive potential energy curve linking two conical intersections, enabling nonadiabatic control over product yields through the state-selection of the reactive flux.

The femtosecond real-time dynamics of the nitrobenzene anion (C6H5NO2 -) in the excited state have been investigated using a recently developed time-resolved photofragment depletion (TRPD) spectroscopic technique, providing molecular-level insight into the C-N bond dissociation pathway leading to ˙C6H5 and NO2 - fragments for the first time. Ultrafast electronic relaxation from the D2 state, prepared at 2.48 eV, to the ground state (D0) is followed by statistical unimolecular dissociation, yielding NO2 - with a lifetime (τ) of approximately 294 ps. This behavior stands in stark contrast to the prompt bond rupture typically observed in conventional dissociative electron attachment (DEA) processes, offering deep insight into the energy flow that governs anionic bond dissociation following electron-molecule collisions.

Excited-state reaction dynamics of the radical anions have been investigated by a newly-developed time-resolved photofragment depletion (TRPD) spectroscopy where the different photodetachment cross-sections of the various anionic species during the reaction process were utilized to unravel their overall temporal evolutions. The otherwise formidable interrogation of the excited-state reaction dynamics of the radical anions, primarily due to the fact that their excited-states are often located above the electron detachment threshold, could be realized here. The shape of the excited-state potential energy surface of I2- has been clearly manifested in the TRPD transients taken at several different probe wavelengths, whereas the ultrafast internal conversion from the optically-excited nonvalence-bound state into the ground or excited valence-bound states of CH3NO2- or (CH3NO2)2-, which is followed by the fast chemical bond dissociation or the rather slow cluster decomposition, has been experimentally investigated for the first time to uncover the overall mechanism of the electron transfer dynamics among different (non)valence orbitals.

Despite its profound significance, the molecular structural changes near the transition state, driven by the vibronic coupling, have remained largely unexplored, leaving a crucial aspect of chemical reactions shrouded in uncertainty. Herein, the dynamical behavior of the reactive flux on the verge of chemical bond breakage was revealed through the spectroscopic characterization of a large amplitude vibrational motion. Highly excited internal rotor states of S1 methylamine (CH3ND2) report on the structural change as the molecule approaches the transition state, indicating that the quasi-free internal rotation is strongly coupled to the reaction coordinate as their energies near the maximum of the reaction barrier for the N-D chemical bond predissociation. Energy-dependent behavior of the rate constant perfectly correlates with that of the molecular structural change in the N-D bond length, providing unprecedented crucial information about how vibrational energy flows into the reaction coordinate on the adiabatic potential energy surfaces.

The specific geometry of a molecule can have a pronounced influence on its chemical reactivity. However, experimental data on reactions of individual molecular isomers are still sparse because they are often difficult to separate and frequently interconvert into one another under ambient conditions. Here, we employ a novel crossed-beam experiment featuring an electrostatically controlled molecular beam combined with a source for radicals and metastables to spatially separate the cis and trans stereoisomers as well as individual rotational states of 1,2-dibromoethene and study their specific reactivities in the chemi-ionisation reaction with excited neon atoms. The experiments reveal pronounced isomeric and rotational specificities in the rates and product branching ratios of the reaction. The present study underlines the importance and combined role of molecular geometry and of rotational motion in the dynamics of chemi-ionisation reactions.

A photodetachment and photoelectron spectroscopic study by employing a cryogenically cooled ion trap combined with a velocity-map imaging setup has been carried out to unravel the vibrational structures and autodetachment dynamics of the dipole-bound states (DBSs) of o-, m-, and p-methylphenolate anions (o-, m-, and p-CH3PhO-). The electron binding energy of the DBS increases monotonically with the increase of the neutral dipole moment to give respective values of 66 +/- 15, 123 +/- 18, or 154 +/- 14 cm-1 for the o-, m-, or p-isomer. The different electron-donating effects of the methyl moieties in the three geometrically different isomers seem to be reflected in the experiment. Mode-specific DBS dynamics of the o-, m-, and p-CH3PhO- complexes have been interrogated by using picosecond time-resolved photoelectron velocity-map imaging spectroscopy. Autodetachment lifetimes of the DBS vibrational Feshbach resonances have been measured and discussed quantitatively using Fermi's golden rule, especially in comparison with those of the phenoxide anion to get insights into the methyl substitution effect on the electron binding dynamics of the metastable DBS.

The S-1 state relaxation dynamics of chlorobenzene (CB), 3-chlorophenol (3-CP), 3-CPH2O, and 2-chlorophenolH2O (2-CPH2O) have been investigated by means of picosecond time-resolved pump-probe spectroscopy in a state-specific manner. For CB, the S-1 state relaxes via the S-1-S-0 internal conversion in the low internal energy region (<2000 cm(-1)), whereas the direct C-Cl bond dissociation channel mediated by the upper-lying repulsive pi sigma(CCl)* state is opened to give the rather sharp increase of the S-1 relaxation rate in the high internal energy region (>2000 cm(-1)). A similar dynamic feature has been observed for 3-CP in terms of the lifetime behavior with an increase in the S-1 internal energy, suggesting that the H atom tunneling dissociation reaction from OH might contribute less compared to the internal conversion, although it is not clear at the present time whether or not the sharp increase of the S-1 relaxation rate in the high internal energy region of 3-CP (>1500 cm(-1)) is entirely due to that of the internal conversion. The fact that the internal conversion is facilitated by the Cl substitution implies that the energetic location of the S-1/S-0 conical intersection should have been strongly influenced by chlorine substitution on the aromatic ring. The approximate energetic location of the saddle point of the S-1(pi pi*)/pi sigma(CCl)* conical intersection along the seam coordinate for CB or 3-CP could be inferred from the energy-dependent S-1 lifetime measurements. It is discussed in comparison with the dynamic role of the S-1(pi pi*)/pi sigma(CCl)* conical intersection, which is strongly influenced by the O-HCl intramolecular hydrogen bond in the rather complicated yet ultrafast S-1 relaxation dynamics of the cis-2-CP. The S-1 lifetimes of 3-CPH2O and 2-CPH2O reveal the importance of the conformational structures, especially in terms of the intramolecular hydrogen bonding

State-specific dynamics of the dipole-bound state (DBS) of the cryogenically cooled deprotonated 4,4'-biphenol anion have been investigated by picosecond time-resolved pump-probe spectroscopy. For DBS vibrational states below the electron-detachment threshold, the relaxation rate is slow to give a lifetime (τ) longer than ∼5 ns, and it is attributed to the nonvalence-to-valence orbital transformation. For the DBS resonances above the detachment threshold, however, the lifetime decreases with the activation of autodetachment, whereas the otherwise zeroth DBS modes seem to be randomized by intramolecular vibrational energy redistribution (IVR), as manifested in the biexponential transients. As the DBS internal energy increases further, the lifetime shows a monotonic decrease to give τ ∼ 50 ps at E'vib ∼ 1700 cm-1. This study demonstrates that IVR may play an important role in the autodetachment dynamics when the density of states rapidly increases with increasing vibrational energy, giving important implications for the electron-transfer dynamics taking place in large biological or astrochemical systems.

Abstract Ultrafast charge carrier dynamics of green‐light emitting InP/ZnSe/ZnS core–shell quantum dots (QDs) with three different ZnSe thickness of 2.0 nm (gQD‐20), 2.4 nm (gQD‐24), or 3.3 nm (gQD‐33) are interrogated by femtosecond transient absorption (TA) and femtosecond stimulated Raman spectroscopy (FSRS). Auger‐type cooling of hot electron into the band‐edge level of InP is clearly manifested in the TA spectra, giving its time constant of ≈222, 300, or 349 fs for gQD‐20, gQD‐24, or gQD‐33, respectively, indicating that the state‐filling to the 1S(e) of InP is significantly slowed down with the increase of the mid shell thickness. The global analysis of the whole TA spectra turns out to be extremely useful to explain the dynamic behavior of the heterogeneous ensemble of single and/or bi‐ (or multi‐) excitons in the presence of the Stark‐shift. The hole‐relaxation dynamics into the band‐edge 1S (h) of the core InP is revealed in the bleaching dynamics of the FSR bands corresponding to the phonon mode of InP or ZnSe, giving the estimated lifetime of 1.0–1.4 ps for gQD‐20. The hole‐relaxation dynamics by the phonon emission seem to be little sensitive to the ZnSe shell thickness.

The H atom tunneling dissociation dynamics of the S1 state of meta- or para-cresol has been investigated by using the picosecond time-resolved pump-probe spectroscopy in a state-specific manner. The S1 state lifetime (mainly due to the H atom tunneling reaction) is found to be mode-dependent whereas it quickly converges and remains constant as the rapid intramolecular vibrational energy redistribution (IVR) starts to participate in the S1 state relaxation with the increase of the S1 internal energy (Eint). The IVR rate and its change with increasing Eint have been reflected in the parent ion transients taken by tuning the total energy (hνpump + hνprobe) just above the adiabatic ionization threshold (so that the dissipation of the initial mode-character could be monitored as a function of the reaction time), indicating that the mode randomization rate into the S1 isoenergetic manifolds exceeds the tunneling rate quite early in terms of Eint for m-cresol (≤∼1200 cm-1) or p-cresol (≤∼800 cm-1) compared to the case of phenol (≤∼1800 cm-1). Though the H atom tunneling dynamics of phenol (S1) seems to be little influenced by the methyl substitution on the either m- or p-position, the IVR rate has been found to be strongly accelerated due to the sharply-increasing (S1) density of states with increasing Eint due to the pivotal role of the low-frequency CH3 torsional mode.

The nature of the electron-binding forces in the dipole-bound states (DBS) of anions is interrogated through experimental and theoretical means by investigating the autodetachment dynamics from DBS Feshbach resonances of ortho-, meta-, and para-bromophenoxide (BrPhO-). Though the charge-dipole electrostatic potential has been widely regarded to be mainly responsible for the electron binding in DBS, the effect of nonclassical electron correlation has been conceived to be quite significant in terms of its static and/or dynamic contributions toward the binding of the excess electron to the neutral core. State-specific real-time autodetachment dynamics observed by picosecond time-resolved photoelectron velocity-map imaging spectroscopy reveal that the autodetachment processes from the DBS Feshbach resonances of BrPhO- anions cannot indeed be rationalized by the conventional charge-dipole potential. Specifically, the autodetachment lifetime is drastically lengthened depending on differently positioned Br-substitution, and this rate change cannot be explained within the framework of Fermi's golden rule based on the charge-dipole assumption. High-level ab initio quantum chemical calculations with EOM-EA-CCSD, which intrinsically takes into account electron correlations, generate more reasonable predictions on the binding energies than density functional theory (DFT) calculations, and semiclassical quantum dynamics simulations based on the EOM-EA-CCSD data excellently predict the trend in the autodetachment rates. These findings illustrate that static and dynamic properties of the excess electron in the DBS are strongly influenced by correlation interactions among electrons in the nonvalence orbital of the dipole-bound electron and highly polarizable valence orbitals of the bromine atom, which, in turn, dictate the interesting chemical fate of exotic anion species.

The dynamic role of the intramolecular hydrogen bond in the S1 relaxation of cis-2-chlorophenol (2-CP) or cis-2-chlorothiophenol (2-CTP) has been investigated in a state-specific manner. Whereas ultrafast internal conversion is dominant for 2-CP, the H-tunneling competes with internal conversion for 2-CTP even at the S1 origin. The S0-S1 internal conversion rate of 2-CTP could be directly measured from the S1 lifetimes of 2-CTP-d1 (Cl-C6H4-SD) as the D-tunneling is kinetically blocked, allowing distinct estimations of tunneling and internal conversion rates with increasing the energy. The internal conversion rate of 2-CTP increases by two times at the out-of-plane torsional mode excitation, suggesting that the internal conversion is facilitated at the nonplanar geometry. It then sharply increases at ∼600 cm-1, indicating that the S1/S0 conical intersection is readily accessible at the extended C-Cl bond length. The strength of the intramolecular hydrogen bond should be responsible for the distinct dynamic behaviors of 2-CP and 2-CTP.