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This article argues that Habermas's transformation of Adorno and Horkheimer's Critical Theory cannot be understood as a departure from Marxism. The authors maintain that Habermas's normative shift transformed Critical Theory into a social ontology and that that is the decisive point of that transformation. They also argue that Adorno's theory was an attempt to surpass the ontology and introduced the notion of "ontological necessity" to understand the social reason that feeds the popularity and success of contemporary ontologies, which differs radically from Habermas's approach. They show that it is possible to recognize "ontological necessity" in Habermas's project and discuss the theoretical and political implications of that. [ABSTRACT FROM AUTHOR]

The time-resolved photodissociation dynamics of CH3I in the A-band has been studied theoretically using a wave packet model including four degrees of freedom, namely the C-I dissociation coordinate, the I-CH3 bending mode, the CH3 umbrella mode, and the C-H symmetric stretch mode. Clocking times and final product state distributions of the different dissociation (nonadiabatic) channels yielding spin-orbit ground and excited states of the I fragment and vibrationless and vibrationally excited (symmetric stretch ν1 and umbrella ν2 modes) CH3 fragments have been obtained and compared with the results of femtosecond velocity map imaging experiments. The wave packet calculations are able to reproduce with very good agreement the experimental reaction times for the CH3(ν1, ν2)+I*(2P1/2) dissociation channels with ν1 = 0 and ν2 = 0,1,2, and also for the channel CH3(ν1 = 0, ν2 = 0)+I(2P3/2). However, the model fails to predict the experimental clocking times for the CH3(ν1, ν2)+I(2P3/2) channels with (ν1, ν2) = (0, 1), (0, 2), and (1, 0), that is, when the CH3 fragment produced along with spin-orbit ground state I atoms is vibrationally excited. These results are similar to those previously obtained with a three-dimensional wave packet model, whose validity is discussed in the light of the results of the four-dimensional treatment. Possible explanations for the disagreements found between theory and experiment are also discussed. [ABSTRACT FROM AUTHOR]

The photodissociation of methyl iodide at different wavelengths in the red edge of the A-band (286–333 nm) has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the methyl fragment in the vibrational ground state (ν=0). The kinetic energy distributions (KED) of the produced CH3(ν=0) fragments show a vibrational structure, both in the I(2P3/2) and I*(2P1/2) channels, due to the contribution to the overall process of initial vibrational excitation in the ν3(C–I) mode of the parent CH3I. The structures observed in the KEDs shift toward upper vibrational excited levels of CH3I when the photolysis wavelength is increased. The I(2P3/2)/I*(2P1/2) branching ratios, photofragment anisotropies, and the contribution of vibrational excitation of the parent CH3I are explained in terms of the contribution of the three excited surfaces involved in the photodissociation process, 3Q0, 1Q1, and 3Q1, as well as the probability of nonadiabatic curve crossing 1Q1←3Q0. The experimental results are compared with multisurface wave packet calculations carried out using the available ab initio potential energy surfaces, transition moments, and nonadiabatic couplings, employing a reduced dimensionality (pseudotriatomic) model. A general qualitative good agreement has been found between theory and experiment, the most important discrepancies being in the I(2P3/2)/[I(2P3/2)+I*(2P1/2)] branching ratios. Inaccuracies of the available potential energy surfaces are the main reason for the discrepancies. [ABSTRACT FROM AUTHOR]

The Ne–Br2(B,v) intermolecular resonances embedded in the continuum of the v=26 vibrational manifold have been characterized. The nature of these states as long-lived, strongly overlapping orbiting resonances supported by centrifugal barriers originated in rotational excitation of Br2 within the complex has been confirmed. The orbiting resonances are found to be highly delocalized in space, both in the radial and angular coordinates, giving rise to long-lived, large-sized Ne-Br2 complexes. [ABSTRACT FROM AUTHOR]

The real time photodissociation dynamics of CH3I from the A band has been studied experimentally and theoretically. Femtosecond pump-probe experiments in combination with velocity map imaging have been carried out to measure the reaction times (clocking) of the different (nonadiabatic) channels of this photodissociation reaction yielding ground and spin-orbit excited states of the I fragment and vibrationless and vibrationally excited (symmetric stretch and umbrella modes) CH3 fragments. The measured reaction times have been rationalized by means of a wave packet calculation on the available ab initio potential energy surfaces for the system using a reduced dimensionality model. A 40 fs delay time has been found experimentally between the channels yielding vibrationless CH3(ν=0) and I(2P3/2) and I*(2P1/2) that is well reproduced by the calculations. However, the observed reduction in delay time between the I and I* channels when the CH3 fragment appears with one or two quanta of vibrational excitation in the umbrella mode is not well accounted for by the theoretical model. [ABSTRACT FROM AUTHOR]

The nonadiabatic photodissociation dynamics of (HI)2 is simulated by applying a wave packet approach which starts from the I*–HI complex (where I* denotes the I(2P1/2) excited electronic state) produced after the photodissociation of the first HI moiety within (HI)2. In the model, two excited electronic potential surfaces corresponding to I*–HI(A 1Π1) and I–HI(A 1Π1), which interact through spin-rotation coupling, are considered. The simulations show that upon photodissociation of HI within I*–HI, the dissociating H fragment undergoes intracluster collisions with the I* atom. Some of these collisional events induce an electronically nonadiabatic transition which causes the deactivation of I* to the I ground electronic state. The probability of such nonadiabatic process is found to be 0.37%. Most of the photodissociation process takes place in the upper excited electronic surface [that of the I*–HI(A 1Π1) complex], where H dissociation is found to be mainly direct or involving weak H/I* intracluster collisions. These weak collisions with high collisional angular momentum, and therefore high collisional impact parameters associated, are responsible for most of the probability of nonadiabatic transitions found. The type of H/I* collisions leading to nonadiabatic transitions appears to be closely related to the nature of the spin-rotation coupling between the two excited electronic states involved. [ABSTRACT FROM AUTHOR]

The sequential photodissociation dynamics of (HI)2 is studied by means of a nonadiabatic wave packet treatment starting from the I*-HI complex. The model reproduces the main experimental findings for photolysis with 266 nm radiation. The results confirm that some of the H atoms dissociated from the I*-HI complex deactivate the I* atom through a H/I* intracluster collision which induces an I*→I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I* excitation energy, equivalent to the I*/I spin-orbit splitting. A most interesting result is the high production of bound I2 fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct. [ABSTRACT FROM AUTHOR]

Quantum-mechanical simulations of the Ne-Br2(B,v′) excitation spectra produced after vibrational predissociation in the v′=20–35 range are reported. The aim is to investigate the signature in the excitation spectra of intermediate resonances lying in the lower v≤v′ vibrational manifolds in order to elucidate their role in the intramolecular vibrational redistribution (IVR) mechanisms in Ne–Br2. By increasing v′, the energy position of the Ne-Br2(B,v′) initial state probes the whole range of the spectrum of v′-1 intermediate resonances, from the continuum resonance states above the Ne+Br2(B,v′-1) dissociation threshold to the resonances below that threshold. In general, the results show that the Ne-Br2(B,v′) initial state couples more strongly to the energetically nearby v′-1 resonances, although coupling to farther away resonances also occurs with appreciable intensity. The excitation spectra reveal a strong overlapping between spectral features, indicating that the intermediate resonances are coupled and interfere between themselves. This coupling generates an interconnected network of intermediate resonances, through which an efficient flow of the initial population leading to IVR takes place. It is found that the density of continuum resonances reaches a maximum in the region just above the Ne+Br2(B,v′-1) threshold, and it decreases gradually with increasing energy above this threshold, as suggested in a previous work. An upper energy limit for the spectrum of v′-1 continuum resonances has been estimated to be about 23–29 cm-1 above the v′-1 dissociation threshold. The excitation spectra reflect that coupling of the initial state with... [ABSTRACT FROM AUTHOR]

Wave-packet simulations of the Ne–Br2(B,υ′) vibrational predissociation dynamics in the range υ′=16–29 are reported. The aim is to interpret recent time-dependent pump-probe experiments [Cabrera et al., J. Chem. Phys. 123, 054311 (2005)]. Good agreement is found between the calculated and the experimental lifetimes corresponding to decay of the Ne–Br2(B,υ′) initial state and to appearance of Br2(B,υ<υ′) products. The simulations show that up to υ′∼22 the dynamics is dominated by direct predissociation, while for higher υ′ levels an indirect intramolecular vibrational relaxation mechanism of dissociation becomes increasingly important. Such a mechanism occurs via coupling of the initial state in the υ′ vibrational manifold to nearly degenerate resonances embedded in the continuum of the lower υ<υ′ manifolds, which act as intermediate doorway states to dissociation. The role of the intermediate resonances manifests itself in multiexponential behavior and oscillations in the time-dependent population curves associated with the initial complex state, the final product states, and the Ne–Br2(B,υ<υ′) intermediate complexes. Analysis of the Ne–Br2(B,υ<υ′) intermediate population shows that the continuum resonances are supported by centrifugal barriers involving excitation of the internal rotation of the complex. We find that the coupling between the intermediate state resonances and the continuum product state wave functions extend to Ne–Br2 distances greater than 15 Å. In the light of the results, a structure of the spectrum of continuum resonances is suggested and discussed. [ABSTRACT FROM AUTHOR]

An empirical intermolecular potential surface is proposed for the He–I2(B 3Πu) complex, modeled as a sum of pairwise He–I Morse interactions plus a three-body interaction term. The potential reproduces with very good agreement the spectral blueshifts and vibrational predissociation lifetimes measured for He–I2(B,υ′) in the range υ′=10–67 of I2 vibrational excitations. In particular, the accuracy achieved in the description of the experimental data for high υ′ levels is attributed to the three-body interaction term included in the potential. The behavior of the potential surface with the I–I separation is analyzed and correlated with the experimental findings. [ABSTRACT FROM AUTHOR]

A full-dimensional, fully coupled wave packet method is proposed and applied to investigate the vibrational predissociation dynamics of the Cl2(B,v′)–He2 complex. Simulations are carried out for the resonance states associated with the v′=10–13 initial vibrational excitations of Cl2, and the results are compared with the available experimental data. A good agreement with experiment is achieved for the resonance lifetimes (typically within experimental error) and the Cl2 fragment rotational distributions. The mechanism of dissociation of the two He atoms is found to be dominantly sequential, through the Δv′=-2 channel. The probabilities obtained for the Δv′=-1 dissociation channel are, however, overestimated due to the use of absorbing boundary conditions combined with finite grid effects. It is suggested that a mechanism of energy redistribution through the couplings between the van der Waals modes of the two weak bonds takes place in the Δv′=-1 dissociation. This mechanism is consistent with the resonance lifetimes and Cl2 rotational distributions predicted. The favorable comparison with most of the experimental data supports the reliability of the potential used to model Cl2(B,v′)–He2, at least in the present range of v′ levels.© 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A full-dimensional, fully coupled wave packet method is proposed and applied to investigate the vibrational predissociation dynamics of the Cl2(B,v′)–He2 complex. Simulations are carried out for the resonance states associated with the v′=10–13 initial vibrational excitations of Cl2, and the results are compared with the available experimental data. A good agreement with experiment is achieved for the resonance lifetimes (typically within experimental error) and the Cl2 fragment rotational distributions. The mechanism of dissociation of the two He atoms is found to be dominantly sequential, through the Δv′=-2 channel. The probabilities obtained for the Δv′=-1 dissociation channel are, however, overestimated due to the use of absorbing boundary conditions combined with finite grid effects. It is suggested that a mechanism of energy redistribution through the couplings between the van der Waals modes of the two weak bonds takes place in the Δv′=-1 dissociation. This mechanism is consistent with the resonance lifetimes and Cl2 rotational distributions predicted. The favorable comparison with most of the experimental data supports the reliability of the potential used to model Cl2(B,v′)–He2, at least in the present range of v′ levels.© 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A wave packet simulation of the ultraviolet photolysis dynamics of Ar-HI(v=0) is reported. Cluster photodissociation is started from two different initial states, namely, the ground van der Waals (vdW) and the first excited vdW bending state, associated with the Ar-I-H and Ar-H-I isomeric forms of the system, respectively. Formation of Ar-I radical products is investigated over the energy range of the cluster absorption spectrum. It is found that the yield of bound Ar-I radical complexes is typically 90%–100% and 70%–80% for the initial states associated with the Ar-I-H and Ar-H-I isomers, respectively. This result is in agreement with the experimentally observed time-of-flight spectrum of the hydrogen fragment produced after Ar-HI photodissociation. The high Ar-I yield is explained mainly by the small amount of energy available for the radical that is converted into internal energy in the photofragmentation process, which enhances the Ar-I survival probability. Quantum interference effects manifest themselves in structures in the angular distribution of the hydrogen fragment, and in pronounced rainbow patterns in the rotational distributions of the Ar-I radical.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A potential energy surface for the ground electronic state of the Ar–HI van der Waals complex is calculated at the coupled-cluster with single and double excitations and a noniterative perturbation treatment of triple excitations [CCSD(T)] level of theory. Calculations are performed using for the iodine atom a correlation consistent triple-ζ valence basis set in conjunction with large-core Stuttgart–Dresden–Bonn relativistic pseudopotential, whereas specific augmented correlation consistent basis sets are employed for the H and Ar atoms supplemented with an additional set of bond functions. In agreement with previous studies, the equilibrium structure is found to be linear Ar–I–H, with a well depth of 205.38 cm-1. Another two secondary minima are also predicted at a linear and bent Ar–H–I configurations with well depths of 153.57 and 151.57 cm-1, respectively. The parametrized CCSD(T) potential is used to calculate rovibrational bound states of Ar–HI/Ar–DI complexes, and the vibrationally averaged structures of the different isomers are determined. Spectroscopic constants are also computed from the CCSD(T) surface and their comparison with available experimental data demonstrates the quality of the present surface in the corresponding configuration regions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ultraviolet photolysis dynamics of Kr–HBr(v=0) is investigated by means of wave packet calculations, focusing on the fragmentation pathway Kr–HBr+hω→H+Kr–Br. Photolysis is simulated by starting from two different cluster initial states, namely the ground van der Waals (vdW) and an excited vdW bending state, associated with the Kr–H–Br and Kr–Br–H isomers, respectively. The results show that, for the two initial states of the cluster, the Kr–Br product yield is lower than that of Ar–Br radicals found in previous studies on Ar–HBr photolysis. Despite this decrease, the Kr–Br yield is found to be still rather high, in particular for the initial excited vdW state of Kr–HBr(v=0). In addition, the Kr–Br product state distributions exhibit a remarkably higher excitation (mainly rotational) than the corresponding Ar–Br distributions. The lower yield and higher excitation of Kr–Br as compared to Ar–Br, are attributed to a larger share of the energy available for the radical going to internal excitation in the case of the Kr–Br product. The different partition of the energy available for Kr–Br also causes significant deviations in the photolysis behavior of Kr–HBr when compared to that of Ar–HBr, in the case of the initial excited vdW state of both clusters. A common feature of the photodissociation of Kr–HBr and Ar–HBr is the manifestation of quantum interference effects in the Kr–Br and Ar–Br rotational state distributions, in the form of pronounced structures of supernumerary rotational rainbows. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]