Intense near-IR Research Articles

Frustrated double and single ionization in a two-electron triatomic molecule H+3

Using a semi-classical model, we study the formation of highly excited neutral fragments during the fragmentation of , a two-electron triatomic molecule, driven by an intense near-IR laser field. To do so, we first formulate a microcanonical distribution for arbitrary one-electron triatomic molecules. We then study frustrated double and single ionization in strongly driven and compute the kinetic energy release of the nuclei for these two processes. Moreover, we investigate the dependence of frustrated ionization on the strength of the laser field as well as on the geometry of the initial molecular state.

Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems.

A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings. The complexes exhibit tunable, intense near-IR (NIR) absorption in the range of 1076-1160 nm with molar absorptivity as high as 25100 M-1 cm-1 in solution. The electronic tunability as well as the desirable solid-state packing arrangements of these systems suggests significant potential as NIR-absorbing materials for optoelectronic applications.

Magnetic feature and near-infrared absorption of a [Pt(mnt)2]--based H-bond supramolecular crystal

A new salt [H2DABCO][Pt(mnt)2]2 (1) (mnt2-=maleonitriledithiolate and H2DABCO2+ is diprotonated 1,4-diazabicyclo[2.2.2]octane) has been synthesized; its crystal structure, magnetic and near-IR absorption properties have been investigated. Two different [Pt(mnt)2]- anions form the strong π-dimers, labeled as Pt(1)-dimer and Pt(2)-dimer, with quite shorter Pt…Pt and S…S distances and molecular plane-to-plane distance (<3.5Å) within a dimer. The [Pt(mnt)2]22- π-dimers are connected through the cations in the strong H-bond manner to form three-dimensional H-bond supramolecular crystal. The salt shows weak paramagnetism in 1.99–300K and this is due to the existence of strong antiferromagnetic coupling within a π-dimer. In addition, a small thermal hysteresis loop is observed at ca. 120K, indicating that a phase transition probably occurs that is further confirmed by variable-temperature IR spectra. Another fascinating functionality of 1 is the intense near-IR absorption in the region of 750–2500nm, and this near-IR absorption feature makes it to be a promising optical material.

Near-infrared unsymmetrical blue and green squaraine sensitizers.

Two novel panchromatic asymmetrical squaraine sensitizers (SPSQ1 and SPSQ2) have been synthesized, characterized and effectively used for TiO2-based dye sensitized solar cells. In a solution, both dyes display a highly intense near-IR absorption (SPSQ1; 651 nm and SPSQ2; 692 nm), the red shifted absorption of SPSQ2 was attributed to the incorporation of the auxiliary acceptor dicyanovinyl unit on the squaraine moiety. Interestingly, the dicyanovinyl unit lowered the LUMO level of SPSQ2, which decreased the band gap and red shifted the absorption when compared to SPSQ1. These dyes possess suitable HOMO and LUMO levels to work as efficient sensitizers in DSSCs. The experimental trends in their optical and electrochemical properties are well matched with the theoretical calculations modeled by TDDFT. The blue and green color of the devices showed their complementary absorption and harvest a greater number of photons from solar flux. Under standard global AM 1.5 G solar conditions, the DSSC based on SPSQ2 exhibited a high power conversion efficiency of 3.1% with a high short circuit current density (JSC) attributed to the broadening of the IPCE spectra in the UV-vis and near-IR regions when compared to SPSQ1 (2.5%).

Single-shot temporal envelope measurement of ultrashort extreme-UV pulses by spatially encoded transmission gating.

Single-shot ultrashort extreme-UV(EUV) pulse waveform measurement is demonstrated by utilizing strong field ionization of H2 gas for transmission gating. A cross-propagating intense near-IR gate pulse ionizes the EUV absorbing H2 molecules into EUV-non-absorbing H2++ (two protons) and creates a time sweep of transmission encoded spatially across the EUV pulse. The temporal envelope is then retrieved from the lopsided spatial profile of the transmitted pulse. This method not only measures EUV temporal envelope for each single shot, but also determines timing jitter and envelope fluctuation statistically, thus is particularly useful for characterizing low-repetition-rate fluctuating EUV/soft x-ray sources.

A trans-1,2 End-On Disulfide-Bridged Iron-Tetracarbene Dimer and Its Electronic Structure.

A disulfide-bridged diiron complex with [Fe-S-S-Fe] core, which represents an isomer of the common biological [2Fe-2S] ferredoxin-type clusters, was synthesized using strongly σ-donating macrocyclic tetracarbene capping ligands. Though the complex is quite labile in solution, single crystals were obtained, and the structure was elucidated by X-ray diffraction. The electron-rich iron-sulfur core is found to show rather unusual magnetic and electronic properties. Experimental data and density functional theory studies indicate extremely strong antiferromagnetic coupling (-J > 800 cm(-1)) between two low-spin iron(III) ions via the S2(2-) bridge, and the intense near-IR absorption characteristic for the [Fe-S-S-Fe] core was assigned to a S → Fe ligand-to-metal charge transfer transition.

Intense near-IR laser induced electron-ion scattering experiment on hydrocarbon molecules

SynopsisWe have measured angle-resolved rescattering photoelectron spectra induced by ultrashort intense near-IR laser pulses at 1200-1650 nm. From the spectra, we have extracted field-free electron-ion differential scattering cross sections and compared them with theoretical calculations.

Recognition of fractional non-innocent feature of osmium coordinated 2,2'-biimidazole or 2,2'-bis(4,5-dimethylimidazole) and their interactions with anions.

Mononuclear complexes [Os(II)(bpy)2(H2L1)](ClO4)2 ([](ClO4)2) and [Os(II)(bpy)2(H2L2)](ClO4)2 ([](ClO4)2) incorporating two free NH protons at the back face of the coordinated H2L, and deprotonated L(2-) bridged symmetric dinuclear complexes [(bpy)2Os(II)(μ-L1(2-))Os(II)(bpy)2)](ClO4)2 ([](ClO4)2) and [(bpy)2Os(II)(μ-L2(2-))Os(II)(bpy)2)](ClO4)2 ([](ClO4)2) (bpy = 2,2'-bipyridine, H2L1 = 2,2'-biimidazole and H2L2 = 2,2'-bis(4,5-dimethylimidazole)) have been characterised. Crystal structures of [](ClO4)2 and the meso (ΔΛ) diastereomeric form of [](ClO4)2 have been determined. The crystal structure of [](ClO4)2 also reveals the hydrogen bonding interactions between its free acidic NH protons and the oxygen atoms of the perchlorate anion in the nearby asymmetric unit. Experimental and DFT/TD-DFT calculations have divulged the non-innocent feature of the doubly deprotonated L(2-) in (3+) and (3+), leading to the resonating formulation of {Os(II)(μ-L(2-))Os(III)} ↔ {Os(II)(μ-L˙(-))Os(II)}, instead of a simple mixed valent situation {Os(II)(μ-L(2-))Os(III)}. The dinuclear complexes (3+) and (3+) display one broad and moderately intense near-IR transition near 1000 nm corresponding to a mixed Os(dπ)/L(π) → Os(dπ)/L(π*) MLLMCT (metal/ligand to ligand/metal charge transfer) transition. Different experimental studies have also established the interaction of (2+) and (2+) with the selective anions.

Characterization of multielectron dynamics in molecules: A multiconfiguration time-dependent Hartree-Fock picture

Using the framework of multiconfiguration theory, where the wavefunction Φ(t) of a many-electron system at time t is expanded as Φ(t)=Σ(I)C(I)(t)Φ(I)(t) in terms of electron configurations {Φ(I)(t)}, we divided the total electronic energy E(t) as E(t)=Σ(I)|C(I)(t)|(2)E(I)(t) . Here E(I)(t) is the instantaneous phase changes of C(I)(t) regarded as a configurational energy associated with Φ(I)(t). We then newly defined two types of time-dependent states: (i) a state at which the rates of population transfer among configurations are all zero; (ii) a state at which {E(I)(t)} associated with the quantum phases of C(I)(t) are all the same. We call the former time-dependent state a classical stationary state by analogy with the stationary (steady) states of classical reaction rate equations and the latter one a quantum stationary state. The conditions (i) and (ii) are satisfied simultaneously for the conventional stationary state in quantum mechanics. We numerically found for a LiH molecule interacting with a near-infrared (IR) field ε(t) that the condition (i) is satisfied whenever the average velocity of electrons is zero and the condition (ii) is satisfied whenever the average acceleration is zero. We also derived the chemical potentials μ(j)(t) for time-dependent natural orbitals ϕ(j)(t) of a many-electron system. The analysis of the electron dynamics of LiH indicated that the temporal change in Δμ(j)(t) ≡ μ(j)(t) + ε(t) · d(j)(t) - μ(j)(0) correlates with the motion of the dipole moment of ϕ(j)(t), d(j)(t). The values Δμ(j)(t) are much larger than the energy ζ(j)(t) directly supplied to ϕ(j)(t) by the field, suggesting that valence electrons exchange energy with inner shell electrons. For H2 in an intense near-IR field, the ionization efficiency of ϕ(j)(t) is correlated with Δμ(j)(t). Comparing Δμ(j)(t) to ζ(j)(t), we found that energy accepting orbitals of Δμ(j)(t) > ζ(j)(t) indicate high ionization efficiency. The difference between Δμ(j)(t) and ζ(j)(t) is significantly affected by electron-electron interactions in real time.

Facile synthesis and enhanced near infrared luminescent properties of CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microstructure.

In this work, we reported the fabrication and characterization of CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microspheres via a facile hydrothermal method in the presence of citric acid and PVP. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectra, and photoluminescence. It's found that citric acid could modulate the nucleation and growth of CaWO4 nanocrystals and enable the co-incorporation of Na+ and Ln3+ (Ln = Nd, Er, and Yb) into CaWO4 lattice. Meanwhile, PVP controlled the assembly of CaWO4 nanocrystals into a core/shell spherical structure. All CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microspheres exhibited intense near-IR luminescence. In comparison with CaWO4:Ln3+/Na+ nanocrystals, the self-assembled core/shell nanoarchitechtures showed highly enhanced IR luminescent properties due to the depressing of surface energy-loss.

Multiple Detachment of the SF6– Molecular Anion with Shaped Intense Laser Pulses

Interaction of molecular SF6(-) anions with intense near-IR laser pulses is found to produce cationic fragments by nonsequential multiple detachment. Dissociative ionization channels that lie more than 20 eV above the threshold energy for double detachment are observed. Mass-resolved product yields are presented and analyzed as a function of the femtosecond laser pulse energy, pulse shape, and polarization ellipticity. The observed strong suppression of multiple detachment by pre-pulses, induced with negative third-order dispersion of the transform-limited fs laser pulse, is interpreted as suppression of a nonsequential process by early single detachment. However, in contrast to the relatively simple picture of a rescattering mechanism characterized by acute sensitivity to polarization ellipticity that dominates double ionization of neutral species and was reported for the atomic F(-) anion, multiple detachment of the molecular anion is found to exhibit only mild ellipticity dependence.

Highly Asymmetric Phthalocyanine as a Sensitizer of Graphitic Carbon Nitride for Extremely Efficient Photocatalytic H2 Production under Near-Infrared Light

Highly asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) with intense near-IR light (650–800 nm) absorption is utilized as a sensitizer to extend the spectral response region of graphitic carbon nitride (g-C3N4) from ∼450 nm to more than 800 nm. Ultraviolet–visible light (UV-vis) diffuse reflectance absorption spectra (DRS), photoluminescence (PL) spectra, time-resolved photoluminescence spectra (TRPS), and energy band structure analyses are adopted to investigate the photogenerated electron transfer process between Zn-tri-PcNc and g-C3N4 on both thermodynamics and dynamics aspects. After optimizing the photocatalytic condition and adding chenodeoxycholic acid (CDCA) as coadsorbent, Zn-tri-PcNc sensitized g-C3N4 photocatalyst shows a H2 production efficiency of 125.2 μmol h–1 under visible/near-IR-light (λ ≥ 500 nm) irradiation, corresponding to a turnover number (TON) of 5008 h–1 with an extremely high apparent quantum yield (AQY) of 1.85% at 700 nm monochromatic light irradiation. The present work...

Picosecond Pulse Radiolysis of the Liquid Diethyl Carbonate

The diethyl carbonate, DEC, is an ester that is used as a solvent in Li-ion batteries, but its behavior under ionizing radiation was unknown. The transient optical absorption spectra, the decay kinetics, and the influence of various scavengers have been studied by using the picosecond laser-triggered electron accelerator ELYSE. In neat DEC, the intense near-IR (NIR) absorption spectrum is assigned to the solvated electron. It is overlapped in the visible range by another transient but longer-lived and less intense band that is assigned to the oxidized radical DEC(-H). The solvated electron molar absorption coefficients and radiolytic yield evolution from 25 ps, the geminate recombination kinetics, and the rate constants of electron transfer reactions to scavengers are determined. The radiolytic mechanism, indicating a certain radioresistance of DEC, is compared with that for other solvents.

Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties

A broad organic-inorganic series of hybrid metal iodide perovskites with the general formulation AMI3, where A is the methylammonium (CH3NH3(+)) or formamidinium (HC(NH2)2(+)) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compounds have been prepared through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. We find that the chemical and physical properties of these materials strongly depend on the preparation method. Single crystal X-ray diffraction analysis of 1-4 classifies the compounds in the perovskite structural family. Structural phase transitions were observed and investigated by temperature-dependent single crystal X-ray diffraction in the 100-400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temperature-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1-4 behave as direct-gap semiconductors with energy band gaps distributed in the range of 1.25-1.75 eV. The compounds exhibit an intense near-IR photoluminescence (PL) emission in the 700-1000 nm range (1.1-1.7 eV) at room temperature. We show that solid solutions between the Sn and Pb compounds are readily accessible throughout the composition range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled as we show for the isostructural series of solid solutions CH3NH3Sn(1-x)Pb(x)I3 (5). The charge transport type in these materials was characterized by Seebeck coefficient and Hall-effect measurements. The compounds behave as p- or n-type semiconductors depending on the preparation method. The samples with the lowest carrier concentration are prepared from solution and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compounds, there is a facile tendency toward oxidation which causes the materials to be doped with Sn(4+) and thus behave as p-type semiconductors displaying metal-like conductivity. The compounds appear to possess very high estimated electron and hole mobilities that exceed 2000 cm(2)/(V s) and 300 cm(2)/(V s), respectively, as shown in the case of CH3NH3SnI3 (1). We also compare the properties of the title hybrid materials with those of the "all-inorganic" CsSnI3 and CsPbI3 prepared using identical synthetic methods.

Unique Ligand-Radical Character of an Activated Cobalt Salen Catalyst That Is Generated by Aerobic Oxidation of a Cobalt(II) Salen Complex

The Co(salen)(X) complex, where salen is chiral N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine and X is an external axial ligand, has been widely utilized as a versatile catalyst. The Co(salen)(X) complex is a stable solid that has been conventionally described as a Co(III)(salen)(X) complex. Recent theoretical calculations raised a new proposal that the Co(salen)(H2O)(SbF6) complex contains appreciable contribution from a Co(II)(salen(•+)) electronic structure (Kochem, A.; Kanso, H.; Baptiste, B.; Arora, H.; Philouze, C.; Jarjayes, O.; Vezin, H.; Luneau, D.; Orio, M.; Thomas, F. Inorg. Chem. 2012, 51, 10557-10571), while other theoretical calculations for Co(salen)(Cl) indicated a triplet Co(III)(salen) electronic structure (Kemper, S.; Hrobárik, P.; Kaupp, M.; Schlörer, N. E. J. Am. Chem. Soc. 2009, 131, 4172-4173). However, there have been no experimental data to evaluate these theoretical proposals. We herein report key experimental data on the electronic structure of the Co(salen)(X) complex (X = CF3SO3(-), SbF6(-), and p-MeC6H4SO3(-)). The X-ray crystallography shows that Co(salen)(OTf) has a square-planar N2O2 equatorial coordination sphere with OTf as an elongated external axial ligand. Magnetic susceptibility data indicate that Co(salen)(OTf) complexes belong to the S = 1 spin system. (1)H NMR measurements provide convincing evidence for the Co(II)(salen(•+))(X) character, which is estimated to be about 40% in addition to 60% Co(III)(salen)(X) character. The CH2Cl2 solution of Co(salen)(X) shows an intense near-IR absorption, which is assigned as overlapped transitions from a ligand-to-metal charge transfer in Co(III)(salen)(X) and a ligand-to-ligand charge transfer in Co(II)(salen(•+))(X). The present experimental study establishes that the electronic structure of Co(salen)(X) contains both Co(II)(salen(•+))(X) and Co(III)(salen)(X) character.

Phenylcyanamidoruthenium Scorpionate Complexes

Nine [Ru(Tp)(dppe)L] complexes, where Tp is hydrotris(pyrazol-1-yl)borate, dppe is ethylenebis(diphenylphosphine), and L is (4-nitrophenyl)cyanamide (NO(2)pcyd(-)), (2-chlorophenyl)cyanamide (2-Clpcyd(-)), (3-chlorophenyl)cyanamide (3-Clpcyd(-)), (2,4-dichlorophenyl)cyanamide (2,4-Cl(2)pcyd(-)), (2,3-dichlorophenyl)cyanamide (2,3-Cl(2)pcyd(-)), (2,5-dichlorophenyl)cyanamide (2,5-Cl(2)pcyd(-)), (2,4,5-trichlorophenyl)cyanamide (2,4,5-Cl(3)pcyd(-)), (2,3,5,6-tetrachlorophenyl)cyanamide (2,3,5,6-Cl(4)pcyd(-)), and (pentachlorophenyl)cyanamide (Cl(5)pcyd(-)), and the dinuclear complex [{Ru(Tp)(dppe)}(2)(μ-adpc)], where adpc(2-) is azo-4,4-diphenylcyanamide, have been prepared and characterized. The crystal structures of [Ru(Tp)(dppe)(Cl(5)pcyd)] and [{Ru(Tp)(dppe)}(2)(μ-adpc)] reveal the Ru(II) ion to occupy a pseudooctahedral coordination sphere in which the cyanamide ligand coordinates to Ru(II) by its terminal nitrogen atom. For both complexes, the cyanamide ligands are planar, indicating significant π mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc(2-). The optical spectra of the nominally ruthenium(III) species [Ru(Tp)(dppe)L](+) were obtained through spectroelectrochemistry measurements and showed an intense near-IR absorption band. Time-dependent density functional theory calculations of these species revealed that oxidation of the ruthenium(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of noninnocent character for these ligands. The spin densities reveal that while the 3-Clpycd species has substantial Ru(II)(3-Clpycd(0)) character, the Cl(5)pycd species is a much more localized ruthenium(III) complex of the Cl(5)pycd monoanion. Some bond order and charge distribution data are derived for these ruthenium(III) species. The near-IR band is assigned as a quite complex mixture of d-d, 4d(π) to L(NCN) MLCT, and L(NCN) to Ru 4d LMCT with even a scorpionate ligand component. Spectroelectrochemistry was also performed on [{Ru(Tp)(dppe)}(2)(μ-adpc)] to generate the mixed-valence state. The intense intervalence transition that is observed in the near-IR is very similar to that previously reported for [{Ru(trpy)(bpy)}(2)(μ-adpc)](2+), where trpy is 2,2':6',2"-terpyridine and bpy is 2,2'-bipyridine, and by analogy identifies [{Ru(Tp)(dppe)}(2)(μ-adpc)](+) as a delocalized mixed-valence complex.

One-dimensional metal-bis-dithiolene compounds with diverse ion-pair arrangements, various magnetic properties and intense near-infrared absorption

Five one-dimensional (1D) ion-pair compounds [4′-R-Bz-NH2Py][M(mnt)2] (mnt2−=maleonitriledithiolate, 4′-R-Bz-NH2Py+=1-(4′-R-benzyl)-4-aminopyridinium and M=Pt, R=F (1), Br (2), I (3), CF3 (4); M=Ni, R=CF3 (5)) were investigated structurally and magnetically. Compounds 2 and 3 are isostructural; 4 and 5 are isomorphic. The magnetic [M(mnt)2]− anions form a 1D tetrameric stack in crystal 1, while dimeric stack in crystals 2–5. Compounds 1, 2 and 4 are diamagnetism over the temperature range 1.8–300K, 3 shows a spin-Peierls-type transition around 124K and 5 displays the typically magnetic character of a low-dimensional antiferromagnetic spin system with a broad maximum centered around 70K. The attempts are failed to fit variable temperature magnetic susceptibility of both 3 in high-temperature phase and 5 over 1.8–350K by an S=½ Heisenberg dimer and 1D alternating chain models, probably due to anisotropic exchange interactions. Five compounds show a broad and intense near-IR absorption band in 750–1600nm region.

Tunable Localized Surface Plasmon Resonances in Tungsten Oxide Nanocrystals

Transition-metal oxide nanocrystals are interesting candidates for localized surface plasmon resonance hosts because they exhibit fascinating properties arising from the unique character of their outer-d valence electrons. WO(3-δ) nanoparticles are known to have intense visible and near-IR absorption, but the origin of the optical absorption has remained unclear. Here we demonstrate that metallic phases of WO(3-δ) nanoparticles exhibit a strong and tunable localized surface plasmon resonance, which opens up the possibility of rationally designing plasmonic tungsten oxide nanoparticles for light harvesting, bioimaging, and sensing.

Near-infrared emission of Yb^3+ through energy transfer from ZnO to Yb^3+ in glass ceramic containing ZnO nanocrystals

Yb(3+)-doped glass and glass ceramic containing ZnO nanocrystals were prepared by the melting-quenching method and subsequent heat treatment. Intense near-IR emission around 1000 nm that originated from the transition of Yb(3+):(2)F(5/2)→(2)F(7/2) was generated as a result of energy transfer from oxygen interstitials in ZnO nanocrystals to Yb(3+) with energy transfer efficiency of about 10%. The quantum yield for the near-IR emission of Yb(3+) under the excitation of 390 nm was about 16.7%. These materials have potential application in achieving high-efficiency Si solar cells via spectrum modification.

Time-resolved Coulomb-explosion imaging of nuclear wave-packet dynamics induced in diatomic molecules by intense few-cycle laser pulses

We studied the nuclear dynamics in diatomic molecules (N${}_{2}$, ${\mathrm{O}}_{2}$, and CO) following their interaction with intense near-IR few-cycle laser pulses. Using Coulomb-explosion imaging in combination with the pump-probe approach, we mapped dissociation pathways of those molecules and their molecular ions. We identified all symmetric and asymmetric breakup channels for molecular ions up to ${\mathrm{N}}_{2}^{5+}$, ${\mathrm{O}}_{2}^{4+}$, and CO${}^{4+}$. For each of those channels we measured the kinetic energy release (KER) spectra as a function of delay between the pump and probe pulses. For both ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$ the asymmetric (3,1) channel is only observed for short (20 fs) delays and completely disappears after that. We interpret this observation as a signature of electron localization taking place in dissociating molecular tri-cations when their internuclear separation reaches about 2.5 times the equilibrium bond length. This is a direct confirmation that electron localization plays an essential role in the universal mechanism of enhanced ionization in homonuclear diatomic molecules. Using classical and quantum mechanical simulations of the time-dependent KER spectra, we identify the pathways and intermediate states involved in the laser-induced dissociation of those molecules.