Showing papers on "Photoexcitation published in 1996"
TL;DR: By increasing the photoexcitation intensity, excited-state interband transitions up to n=5 can be observed in photoluminescence, allowing the Fermi level to be raised by more than 200 meV due to the combined large intersublevel spacing and the low density of states.
Abstract: We present radiative lifetime measurements of excited states in semiconductor self-assembled quantum dots. By increasing the photoexcitation intensity, excited-state interband transitions up to n=5 can be observed in photoluminescence. The dynamics of the interband transitions and the intersublevel relaxation in these zero-dimensional energy levels lead to state filling of the lower-energy states, allowing the Fermi level to be raised by more than 200 meV due to the combined large intersublevel spacing and the low density of states. The decay time of each energy level obtained under various excitation conditions is used to evaluate the intersublevel thermalization time. \textcopyright{} 1996 The American Physical Society.
219 citations
TL;DR: In this article, the absorption, photoexcitation and internal and external luminescence efficiencies for Alq3 films grown by vacuum deposition have been measured accurately for the first time, and the internal quantum efficiency was found to be (32 ± 2)% independent of film thickness from 100 A to 1.35 μm.
219 citations
TL;DR: In this paper, the energy transfer from the accessory bacteriochlorophylls (B) to the special pair (P) in the photosynthetic reaction center has been time resolved with pump−probe polarization anisotropy measurements using 20−25 fs duration pulses near 800 nm.
Abstract: The energy transfer from the accessory bacteriochlorophylls (B) to the special pair (P) in the photosynthetic reaction center has been time resolved with pump−probe polarization anisotropy measurements using 20−25 fs duration pulses near 800 nm. The experiments were carried out at low pulse energies (500 pJ in a 34 μm spot), low repetition rates (5 kHz), and high sample flow velocities (100 cm/s) to avoid artifacts from saturation and photoexcitation of incompletely relaxed reaction centers. The pump excitation corresponds to 1.4 × 106 photons/μm2: the “saturation intensity” for the charge separation quantum yield is 3 × 107 photons/μm2. Magic angle pump−probe transients can be satisfactorily fit as biexponential, with an ∼120 fs bleach decay followed by a 2.8 ps bleach rise. (An ∼400 fs bleach decay seen in several previous experiments arises from unrelaxed reaction centers.) The initial pump−probe anisotropy is 0.4 and decays with an ∼80 fs time constant, which we attribute to dipole reorientation by e...
209 citations
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01 Jan 1996TL;DR: In this paper, the authors discuss the molecular applications of quantum defect theory and display two molecular spectra exhibiting striking effects due to both preionization and predissociation, which is called autoionization or preissociation if the continuum is associated with nuclear rather than with electronic motion.
Abstract: Publisher Summary This chapter discusses the molecular applications of quantum defect theory. Quantum defect theory provides a unified description of discrete and continuous spectra in terms of the same parameters pertaining to the physics at short range. It accounts for the Rydberg structures as well as for their decay into the continuum. This decay is called preionization (or autoionization), or predissociation if the continuum is associated with nuclear rather than with electronic motion. It displays two molecular spectra exhibiting striking effects due to both preionization and predissociation. Both spectra result from photoexcitation of nitric oxide and they cover the same wavelength region. The upper spectrum is a recording of the ion current resulting after excitation just above the ionization threshold. The small peaks superimposed on the flat continuum are Rydberg structures whose presence reveals the occurrence of preionization. The lower trace is an absorption spectrum taken under comparable experimental resolution. The significant different appearance of the two spectra reveals that a second decay channel, corresponding to production of neutral atomic fragments, must also interfere. Moreover, the different appearance of the Rydberg peaks in the two spectra indicates that predissociation is strong and competes with preionization.
169 citations
TL;DR: Possibility of considerable enhancement of two photon absorption even in the presence of Doppler broadening is demonstrated.
Abstract: The possibility of transparency against two photon absorption is predicted. Detailed absorption profiles under different conditions of the control laser are given. A novel explanation of the absorption minimum is given in terms of the two photon Fermi golden rule and the dressed states. Possibility of considerable enhancement of two photon absorption even in the presence of Doppler broadening is demonstrated.
154 citations
TL;DR: In this paper, the authors reported time-resolved excited state absorption measurements which demonstrate sub-picosecond photoinduced electron transfer using soluble derivatives of poly(pphenylene vinylene) as donors blended with a functionalized fullerene (methanofullerene) as acceptor.
Abstract: We report time‐resolved excited state absorption measurements which demonstrate subpicosecond photoinduced electron transfer using soluble derivatives of poly(p‐phenylene vinylene) as donors blended with a functionalized fullerene (methanofullerene) as acceptor. The subpicosecond photoinduced absorption spectra of the polymer/methanofullerene blends show that electron transfer from the donor to the acceptor occurs within a picosecond of photoexcitation of the conjugated polymer. Precise determination of the electron transfer dynamics was obtained by monitoring the dichroic ratio. The charge separated state is metastable and persists into the millisecond time domain, yielding an asymmetry of 10 orders of magnitude between the forward and reverse electron transfer times. The increased miscibility of the functionalized methanofullerene with the conjugated polymer is important for preparation of films with sufficiently high acceptor concentrations for practical devices based on photoinduced charge separation.
150 citations
TL;DR: A ring pattern is observed, with a number of dark rings which is analogous to the first parabolic quantum number of the LoSurdo-Stark problem.
Abstract: ${\mathrm{Br}}^{\ensuremath{-}}$ ions undergo photodetachment in the presence of an electric field. As a result of the photoexcitation process, the emitted electron's wave function extends to infinity, but inside a paraboloid elongated in the direction of the field. A position-sensitive detector set across the electron emission axis makes it possible to image the transverse factor of the atomic wave function. A ring pattern is observed, with a number of dark rings which is analogous to the first parabolic quantum number of the LoSurdo-Stark problem.
150 citations
TL;DR: In this paper, the reaction and relaxation processes induced by photoexcitation of an aqueous chloride ion are studied with quantum molecular dynamics simulations by means of theoretical transient and stationary absorption spectra.
Abstract: Reaction and relaxation processes induced by photoexcitation of an aqueous chloride ion are studied with quantum molecular dynamics simulations. A predominant channel leading to a metastable hydrated electron‐chlorine pair is found. By means of theoretical transient and stationary absorption spectra, the solvent reorganization involved in the charge repartitioning is discussed. The dissipation of excess electron kinetic energy by surrounding water molecules plays an essential role in the equilibration of an electron‐atom pair. For this intermediate species, two competing reaction pathways are identified. One is the barrier‐impeded dissociation yielding a hydrated electron. Shape and height of the free energy barrier determined by quantum umbrella sampling point to a diffusion controlled electron photodetachment. The other channel is the geminate recombination via a nonadiabatic transition for which a self‐consistent and fully dynamical treatment of the solvent electronic polarization is found to be important. From the rate constants computed for the individual channels, a kinetic model is derived to explain time‐dependent spectral signatures and electron escape yields recently observed in photodetachment experiments on aqueous halides.
109 citations
TL;DR: The electron spin dynamics associated with intramolecular electron transfer in a photosynthetic model system, which consists of a linear structure of the type A-B-C, is described in this article.
Abstract: The electron spin dynamics associated with intramolecular electron transfer in a photosynthetic model system, which consists of a linear structure of the type A-B-C, is described. In this structure, donor A is a p-methoxyaniline, chromophore B is a 4-amino-1,8-naphthalimide, and acceptor C is a 1,4:5,8-naphthalenediimide. This supramolecular electron donor−acceptor array was isotropically oriented in toluene, and anisotropically oriented in liquid crystal matrices, and studied by time-resolved electron paramagnetic resonance spectroscopy. Photoexcitation of B results in a two-step electron transfer to yield the radical ion pair, A•+-B-C•-. Charge recombination within A•+-B-C•- produces a molecular triplet state, A-B-3*C, which exhibits the unique spin-polarized electron paramagnetic resonance signal that has been observed only in photosynthetic reaction-center proteins.
109 citations
TL;DR: A Monte Carlo study of the relaxation and dissociation dynamics of optical excitations in poly(p-phenylenevinylene) gives a complete picture of the excitation dynamics, the relevant parameters of the spectral relaxation, and the trapping processes involved.
Abstract: We present a Monte Carlo study of the relaxation and dissociation dynamics of optical excitations in poly(p-phenylenevinylene). The quantitative comparison with experimental data gives a complete picture of the excitation dynamics, the relevant parameters of the spectral relaxation, and the trapping processes involved. Our simulations are extended to include the primary step of the dissociation of a neutral photoexcitation in an electric field. The comparison with the results of field-induced photoluminescence quenching experiments enables us to understand the dissociation dynamics and to determine the exciton binding energy to 0.3\ifmmode\pm\else\textpm\fi{}0.1 eV. \textcopyright{} 1996 The American Physical Society.
95 citations
TL;DR: In this article, the authors reported photocurrent and photoluminescence measurements on blends of the organometallic polymer Pt-poly-yne and C 60, and showed that triplet excitons with a binding energy of at least 0.8 eV are created after photoexcitation of Pt-Poly-Yen.
TL;DR: It is shown that charges trapped at depths of 0.1 and 0.4 eV govern the observed charge transport and change in the absorption upon photoexcitation and in particular that the temperature dependence of the PIA intensity in the millisecond range reflects thermal effects on transport processes.
Abstract: We present measurements of thermally stimulated currents and photoinduced absorption (PIA) in a planarized form of poly(para-phenylene). Due to the high intrachain order of the samples and their narrow distribution of effective conjugation lengths the density of states shows a very steep onset at the band gap energy. This is the prerequisite for detecting distinct trap levels and to determine their concentration and depth. We show that charges trapped at depths of 0.1 and 0.4 eV govern the observed charge transport and change in the absorption upon photoexcitation and in particular that the temperature dependence of the PIA intensity in the millisecond range reflects thermal effects on transport processes. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the photoionization of neutral liquid helium droplets was studied using synchrotron radiation at photon energies ranging from 15 to 30 eV, and the mass spectra as well as total and mass selective ion yields were measured as a function of the photon energy for different droplet sizes.
Abstract: The photoionization of neutral liquid helium droplets (mean particle number 〈N〉=102–107) was studied using synchrotron radiation at photon energies ranging from 15 to 30 eV. Mass spectra as well as total and mass selective ion yields were measured as a function of the photon energy for different droplet sizes. The experiments indicate that ionization occurs not only by a direct process at photon energies above the atomic ionization potential but also at energies below the threshold by an autoionization process. The latter ionization mechanism proceeds via the electronically excited states of the neutral droplet, which show a strong neutral droplet size dependence. For large neutral droplets HeN(〈N〉≳104) retarding field measurements established that a predominant part of the total ion yield results from larger cluster ions He+k(k≳103). These measurements also show that a decay by fluorescence emission is much more probable than one by ionization following the photoexcitation process. In droplets with embed...
TL;DR: In this paper, a Gaussian plus biexponential decay of the solvent response function is characterized by a Gaussian plus biclastic decomposition, indicating the importance of symmetry of both the ground and excited states in determining the resulting solvent response.
Abstract: Quantum nonadiabatic molecular dynamics simulations are used to explore the molecular details surrounding photoexcitation of solvated electrons in deuterated water. The results are compared to previous studies in normal water [B. J. Schwartz and P. J. Rossky, J. Chem. Phys. 101, 6902, 6917 (1994)] to elucidate the nature of the isotope effect on both the solvation and nonadiabatic relaxation dynamics. The solvent spectral density couples differently to the individual energy levels than to the quantum energy gap, indicating the importance of the symmetry of both the ground and excited states in determining the resulting solvent response. The solvation dynamics are characterized by a Gaussian plus biexponential decay. Deuteration has little effect on the Gaussian component or long time exponential decay of the solvent response function, but a ∼20% isotope effect is observed on the faster exponential decay. The solvent response following nonadiabatic relaxation is found to be much more rapid than that follow...
TL;DR: The potential of dimethylsilylene and isopropylidene U-spacers as bridges for photoinduced charge transfer (CT) in 4-cyano-4'-dimethylamino)- and 4-cyclo-methoxy-substituted diphenyldimethylsilanes and 2,2-diphen- ylpropanes was studied in this article.
Abstract: The potential of dimethylsilylene and isopropylidene U-spacers as bridges for photoinduced charge transfer (CT) in 4-cyano-4'-(dimethylamino)- and 4-cyano-4'-methoxy-substituted diphenyldimethylsilanes and 2,2-diphen- ylpropanes was studied. Fluorescence solvatochromism and time-resolved microwave conductivity measurements show that upon photoexcitation a charge separated state (D ¥+ UA ¥- )* is populated in all compounds. Excited state dipole moments for a given donor-acceptor combination are, irrespective of the bridge, equal. The CT states of the silanes are however lying at lower energies, implying that the presence of silicon thermodynamically facilitates the CT process. Cyclic voltammetry data of model compounds show that this is a consequence of the lowering of the acceptor reduction potential by the silicon bridge. It was however inferred from radiative decay rates that the electronic coupling between the CT and locally excited states as well as the coupling between the ground and CT state is larger for the carbon-bridged compounds. As shown by both solution and solid state electronic spectra and radiative decay rates, the photophysics of the DUA compounds are dominated by intensity borrowing of the CT transitions from transitions localized in the DU and UA chromophores.
TL;DR: The nearly identical PA response of all forms of the polymer reflects the generation of the same primary photoexcitation, a Coulombically bound intrachain singlet exciton, and the absence of exotic species such as interchain excimers.
Abstract: We present results of picosecond photoinduced absorption (PA) and time-resolved photoluminescence studies on solid and solution forms of poly(p-pyridyl vinylene). The nearly identical PA response of all forms of the polymer reflects the generation of the same primary photoexcitation, a Couloumbically bound intrachain singlet exciton, and the absence of exotic species such as interchain excimers. The time dependence of the PA points to direct intersystem crossing as the origin of triplet excitons, ruling out generation of free carriers as a precursor to exciton formation.
TL;DR: In this paper, the photobleach spectrum changes and its maximum red shift with delay time due to the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps).
Abstract: Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440−740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.
TL;DR: In this paper, a natural connection between mesoscale response to incident laser light and microscopic potentials is made, which describes bond-weakening as electrons are promoted from bonding to anti-bonding orbitals by photon absorption.
TL;DR: In this article, the absolute absorption cross section of C60 in the gas phase (830-870 K) was measured as a function of the photon energy (3.5-11.4 eV) (absorption spectrum).
Abstract: The absolute absorption cross section of C60 in the gas phase (830–870 K) was measured as a function of the photon energy (3.5–11.4 eV) (absorption spectrum). Absorption peaks at 7.87, 8.12, 8.29, 9.2 eV and a dip at 8.45 eV observed are assigned as Feshbach resonances in the photoexcitation involving superexcited states. The superexcited states responsible for the 7.87, 8.12, and 9.2 eV peaks are assigned to be core‐excited Rydberg states converging to the second, the third and the fourth ionization limits of C60 (8.89, 9.12, 10.82–11.59 eV), respectively. The 8.29 eV peak is considered to originate from vibrational excitation of a totally symmetric pentagonal pinch mode of the superexcited state responsible for the 8.12 eV peak. Further, a relative photoionization quantum yield was estimated from the absorption cross section measured and the relative photoionization cross section reported. The yield increases particularly in the vicinity of 8 eV in accordance with a high efficiency of autoionization of ...
TL;DR: In this paper, a novel all-optical light modulation was proposed based on photoinduced changes of an imaginary part of complex refractive index in guided wave geometry, and very fast and repeated modulation of a reading beam (reflected intensity) was demonstrated at the incident angle corresponding to a sharp guided wave resonance using phthalocyanine-doped poly(vinyl alcohol) film as a photoresponsive layer and a nanosecond pulsed laser as a writing beam.
Abstract: A novel all‐optical light modulation has been proposed based on photoinduced changes of an imaginary part of complex refractive index in guided wave geometry. Very fast and repeated modulation of a reading beam (reflected intensity) was demonstrated at the incident angle corresponding to a sharp guided wave resonance using phthalocyanine‐doped poly(vinyl alcohol) film as a photoresponsive layer and a nanosecond pulsed laser as a writing beam. Such responses were mainly due to the formation and decay of excited triplet phthalocyanine. The rise and fall time was markedly improved as compared with previous systems based on photothermal changes of the refractive index.
TL;DR: It is found that the efficiency of the exciton-formation process and the temporal evolution of the resulting population are sensitive to the excitation energy.
Abstract: The energy relaxation of coupled free-carrier and exciton populations in semiconductors after low-density ultrafast optical excitation is studied through a kinetic approach. The set of semiclassical Boltzmann equations, usually written for electron and hole populations only, is complemented by an additional equation for the exciton distribution. The equations are coupled by reaction terms describing phonon-mediated exciton binding and dissociation. All the other relevant scattering mechanisms, such as carrier-carrier, carrier-phonon, and exciton-phonon interactions, are also included. The resulting system of rate equations in reciprocal space is solved by an extended ensemble Monte Carlo method. As a first application, we show results for the dynamics of bulk GaAs in the range from 1 to \ensuremath{\sim}200 ps after photoexcitation. The build-up of an exciton population and its sensitivity to the excitation conditions are discussed in detail. As a consequence of the pronounced energy dependence of the LO-phonon-assisted transition probabilities between free-pair states and excitons, it is found that the efficiency of the exciton-formation process and the temporal evolution of the resulting population are sensitive to the excitation energy. We discuss the effects on luminescence experiments. \textcopyright{} 1996 The American Physical Society.
TL;DR: Using an ensemble Monte Carlo simulation, the results show that the intersubband decay of electrons from the first excited subband into the ground subband is limited by ionized impurity scattering during the photoexcitation process, and the interSubband Decay of electrons is nonexponential.
Abstract: Using an ensemble Monte Carlo simulation, we have investigated intersubband relaxation of photoexcited electrons in GaAs/Al x Ga 1−x As quantum wells having a subband separation smaller than the polar optical phonon energy. Intra- and intersubband scattering through polar optical phonons, acoustic phonons, ionized impurities, and electron-electron scattering are included in the simulation. A comparison is made to recent time-resolved pump and probe experiments performed on uniformly doped samples in which good agreement between theory and experiment is obtained. Our results show that the intersubband decay of electrons from the first excited subband into the ground subband is limited by ionized impurity scattering during the photoexcitation process. Polar optical phonon emission also contributes considerably to the electron decay and occurs from the thermal tail of the heated distribution function in both subbands. Intersubband scattering by intercarrier interaction plays a lesser role for the decay. The heating of the distribution functions is due to ionized impurity intersubband scattering and electron-electron intrasubband scattering, which convert potential energy of an electron into kinetic energy. These mechanisms drive both subbands rapidly towards a single quasiequilibrium distribution with a common electron temperature and chemical potential after the pulse is over. The cooling rate of this distribution function, which governs the intersubband decay, depends initially on the energy relaxation through polar optical phonons, whereas at much longer times acoustic phonon scattering predominates. Thus, the intersubband decay of electrons is nonexponential.
TL;DR: In this article, the polarized absorption spectra of Zn2SiO4 willemite crystals doped with Co2+ consist of three band systems in the near-infrared and visible spectra region centered at 3800, 7000, and 17000 cm−1, respectively.
TL;DR: In this article, the femtosecond transient absorption spectroscopy was used to study the ultrafast dynamics of chlorine dioxide (OClO) photochemistry in aqueous solution.
Abstract: The ultrafast dynamics of chlorine dioxide (OClO) photochemistry in aqueous solution was studied by femtosecond transient absorption spectroscopy. Following the photoexcitation of OClO at 395 nm, the transient absorption dynamics were probed at 12 different wavelengths ranging from 350 to 700 nm. The transient absorption features observed in the visible wavelengths are assigned to correspond to the vibrationally hot photoisomer ClOO*. The spectral dynamics reveal the vibrational relaxation of this molecule in its ground electronic state. The total vibrational energy relaxation occurs within ∼9 ps. The dynamics of the formation of chlorine atom was examined by measuring the absorption dynamics in the 350−390 nm range. The time constant for Cl formation is calculated to be ∼200 ps. The data show that the dominant pathway for Cl formation is via the isomerized ClOO molecule. No fast component for Cl is detected, indicating that the ClOO molecule reaches thermal equilibrium before dissociating into Cl and O2.
TL;DR: In this paper, the unimolecular decomposition of expansion-cooled NO3 has been investigated in the threshold regime of the NO+O2 channel, where the NO yield goes to zero rapidly above the O+NO2 threshold (17,780−17,090 cm−1).
Abstract: The unimolecular decomposition of expansion‐cooled NO3 has been investigated in the threshold regime of the NO+O2 channel. Photoexcitation in the region 16 780–17 090 cm−1 (596–585 nm) prepares ensembles of molecular eigenstates, each of which is a mixture of the B 2E′ bright state and lower electronic states. The X 2A2′ ground state is believed to be the probable terminus of 2E′ radiationless decay, though participation of A 2E″ is also possible. For these photon energies, unimolecular decomposition occurs exclusively via the NO+O2 channel, and NO yield spectra and state distributions have been obtained. The yield spectra are independent of the rotational state monitored, as expected for a large reverse barrier. The state distributions are insensitive to the photolysis photon energy and can be rationalized in terms of dynamical bias. The NO yield goes to zero rapidly above the O+NO2 threshold (17 090±20 cm−1). Because of tunneling, the NO+O2 channel does not have a precise threshold; the value 16 780 cm−...
TL;DR: Data is reported for the first measurement of even-parity hollow lithium states produced by triple photoexcitation of laser-excited lithium atoms and partial photoionization cross sections.
Abstract: Photoelectron data are reported for the first measurement of even-parity hollow lithium states produced by triple photoexcitation of laser-excited lithium atoms. Calculations using the {ital R}-matrix approximation of the energy of these states and partial photoionization cross sections are also reported. Experiment and theory are in excellent agreement on a relative scale. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this article, the size-dependent kinetics of exciton recombination in a III-V quantum dot system, InP, were investigated and various frequency dependent quantum yields as a function of temperature, frequency dependent luminescence decay curves, and time-gated emission spectra.
Abstract: We report here on the size‐dependent kinetics of exciton recombination in a III–V quantum dot system, InP. The measurements reported include various frequency dependent quantum yields as a function of temperature, frequency dependent luminescence decay curves, and time‐gated emission spectra. This data is fit to a three‐state quantum model which has been previously utilized to explain photophysical phenomena in II–VI quantum dots. The initial photoexcitation is assumed to place an electron in a (delocalized) bulk conduction band state. Activation barriers for trapping and detrapping of the electron to surface states, as well as activation barriers for surface‐state radiationless relaxation processes are measured as a function of particle size. The energy barrier to detrapping is found to be the major factor limiting room temperature band‐edge luminescence. This barrier increases with decreasing particle size. For 30 A particles, this barrier is found to be greater than 6 kJ/mol—a barrier which is more than an order of magnitude larger than that previously found for 32 A CdS nanocrystals.
TL;DR: In this article, an increase of the translational temperature after photoexcitation to the electronically excited state of Ni2+ in aqueous solution was detected using a time-resolved transient lens method from the picosecond to millisecond time scale.
Abstract: An increase of the translational temperature after photoexcitation to the electronically excited state of Ni2+ in aqueous solution is detected using a time‐resolved transient lens method from the picosecond to millisecond time scale. Besides a large lens signal due to the volume expansion of water in the submicrosecond time range, two other lens signals are observed at an initial part of the signal. During the pump laser pulse, a convex lens signal is observed, which is attributed to the optical Kerr lens signal. After the pulse, a concave lens is created, which remains a nearly constant amplitude until the density lens signal appears. The signal is attributed to the temperature lens signal, which originates from the heat energy by the nonradiative transition of the excited state. It is found that the signal rises within 3 ps after the photoexcitation, which indicates that the temperature rise is very fast. After the fast rise, another slower dynamics (500 ps) is observed and the deactivation processes of Ni2+ in aqueous solution are discussed based on these results.
TL;DR: In this paper, the first time electron spin resonance studies are reported for various isotopomers of GaH2 and HGaCH3 and the radicals were generated in neon matrices at 4 K by the ultraviolet photoexcitation of Ga which undergoes insertion reactions with H2 and CH4.
Abstract: First time electron spin resonance studies are reported for various isotopomers of GaH2 and HGaCH3. The radicals were generated in neon matrices at 4 K by the ultraviolet photoexcitation of Ga which undergoes insertion reactions with H2 and CH4. Ab initio calculations with a large uncontracted basis and configuration interaction with all single excitations from the spin‐restricted Hartree–Fock configuration gave good agreement with the experimental results and supported the free atom comparison method interpretation of the hyperfine interactions. A comparison with similar radicals is presented, including BH2, AlH2, HAlCH3, HAlOH, and AlH+.
TL;DR: In this paper, the electronic properties of ground and excited state sodium nitrate were investigated using ab initio quantum mechanical methods and the results of these calculations were used to explain the photoexcitation/desorption mechanism and support the conclusions of an earlier experimental investigation of the laser desorption of NO from single-crystal NaNO{sub 3}.
Abstract: This theoretical study uses ab initio quantum mechanical methods to investigate the electronic properties of ground and excited state sodium nitrate. We calculated electronic properties of the crystalline material for bulk, clean, and defected surfaces. The results of these calculations are used to explain the photoexcitation/desorption mechanism and support the conclusions of an earlier experimental investigation of the laser desorption of NO from single-crystal sodium nitrate. The calculations indicate that the electronic structure of the bulk and cleavage surface are virtually identical (i.e., no shift in the resonant absorption profile is expected). This finding is consistent with the experimental results on the wavelength dependence of NO desorption yields for crystalline NaNO{sub 3}. However, changes in the absorption manifold are found to accompany the removal of external nitrate oxygens (producing surface nitrite groups). The presence of these chemical defects causes states to appear in the band gap producing a red shift in the absorption band. These calculations also indicate that the transition energies of the nitrate ion are unaffected by the presence of the surrounding ions. 34 refs., 8 figs., 2 tabs.