Vibronic coupling in the ground and excited states of the imidazole radical cation.

Vibronic interactions in the ground and two excited states of the imidazole radical cation, X2A″ (π-1), A2A' (nσ-1), and B2A″ (π-1), and the associated nuclear dynamics were studied theoretically. The results were used to interpret the recent photoelectron measurements [M. Patanen et al., J. Chem. Phys. 155, 054304 (2021)]. The present high-level electronic structure calculations employing, in particular, the single, double, and triple excitations and equation-of-motion coupled-cluster method accounting for single and double excitation approaches and complete basis set extrapolation technique for the evaluation of the vertical ionization energies of imidazole indicate that the A 2A' and B 2A″ states are very close in energy and subject to non-adiabatic effects. Our modeling confirms the existence of pronounced vibronic coupling of the A 2A' and B 2A″ states. Moreover, despite the large energy gap of nearly 1.3 eV, the ground state X 2A″ is efficiently coupled to the A 2A' state. The modeling was performed within the framework of the three-state linear vibronic coupling problem employing Hamiltonians expressed in a basis of diabatic electronic states and parameters derived from ab initio calculations. The ionization spectrum was computed using the multi-configuration time-dependent Hartree method. The calculated spectrum is in good agreement with the experimental data, allowing for some interpretation of the observed features to be proposed.

Vibronic coupling in the ground and excited states of the pyridine radical cation.

Vibronic interactions in the pyridine radical cation ground state, 2A1, and its lowest excited states, 2A2 and 2B1, are studied theoretically. These states originate from the ionization out of the highest occupied orbitals of pyridine, 7a1 (nσ), 1a2 (π), and 2b1 (π), respectively, and give rise to the lowest two photoelectron maxima. According to our previous high-level ab initio calculations [Trofimov et al., J. Chem. Phys. 146, 244307 (2017)], the 2A2 (π-1) excited state is very close in energy to the 2A1 (nσ-1) ground state, which suggests that these states could be vibronically coupled. Our present calculations confirm that this is indeed the case. Moreover, the next higher excited state, 2B1 (π-1), is also involved in the vibronic interaction with the 2A1 (nσ-1) and 2A2 (π-1) states. The three-state vibronic coupling problem was treated within the framework of a linear vibronic coupling model employing parameters derived from the ionization energies of pyridine computed using the linear response coupled-cluster method accounting for single, double, and triple excitations (CC3). The potential energy surfaces of the 2A1 and 2A2 states intersect in the vicinity of the adiabatic minimum of the 2A2 state, while the surfaces of the 2A2 and 2B1 states intersect near the 2B1 state minimum. The spectrum computed using the multi-configuration time-dependent Hartree (MCTDH) method accounting for 24 normal modes is in good qualitative agreement with the experimental spectrum of pyridine obtained using high-resolution He I photoelectron spectroscopy and allows for some assignment of the observed features.

An experimental and theoretical study of the photoelectron spectra of cis-dichloroethene: Valence shell vertical ionization and vibronic coupling in the low-lying cationic states.

The valence shell photoelectron spectrum of cis-dichloroethene has been studied both experimentally and theoretically. Photoelectron spectra have been recorded with horizontally and vertically plane polarized synchrotron radiation, thereby allowing the anisotropy parameters, characterizing the angular distributions, to be determined. The third-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function has been employed to compute the complete valence shell ionization spectrum. In addition, the vertical ionization energies have been calculated using the outer valence Green's function (OVGF) method and the equation-of-motion coupled-cluster, with single and double substitutions for calculating ionization potentials (EOM-IP-CCSD) model. The theoretical results have enabled assignments to be proposed for most of the structure observed in the experimental spectra, including the inner-valence regions dominated by satellite states. The linear vibronic coupling model has been employed to study the vibrational structure of the lowest photoelectron bands, using parameters obtained from ab initio calculations. The ground state optimized geometries and vibrational frequencies have been computed at the level of the second-order Møller-Plesset perturbation theory, and the dependence of the ionization energies on the nuclear configuration has been evaluated using the OVGF method. While the adiabatic approximation holds for the X̃2B1 state photoelectron band, the Ã2B2, B̃2A1, and C̃2A2 states interact vibronically and form a complex photoelectron band system with four distinct maxima. The D̃2B1 and Ẽ2B2 states also interact vibronically with each other. The potential energy surface of the D̃2B1 state is predicted to have a double-minimum shape with respect to the out-of-plane a2 deformations of the molecular structure. The single photoelectron band resulting from this interaction is characterized by a highly irregular structure, reflecting the non-adiabatic nuclear dynamics occurring on the two coupled potential energy surfaces forming a conical intersection close to the minimum of the Ẽ2B2 state.

Ab Initio Benchmark Study of Nonadiabatic S1-S2 Photodynamics of cis- and trans-Hexatriene.

The dynamics of the nonadiabatically coupled lowest singlet excited states of cis- and trans-hexatriene are studied theoretically, in a comprehensive electronic structure and quantum dynamical investigation. At the ground state equilibrium geometry the relevant S2 and S1 states carry the A1 (Ag) and B2 (Bu) symmetry labels, for the cis (trans) isomer. Various high-level electronic structure methods are used, including the recently reparametrized DFT/MRCI method, and the results are critically compared. Key parameters of interest are the vertical energy gap and the strength of vibronic coupling between the interacting electronic states. To estimate their influence, suitable comparison calculations are performed. The results are used as the basis for quantum dynamical calculations on the UV absorption spectrum and electronic population transfer involving the S1 and S2 states. Up to nine nonseparable degrees of freedom are included in the calculations. The experimental UV absorption spectrum in the 5-5.2 eV energy range can be very well reproduced. The time-dependent wavepacket propagations reveal a population transfer on the order of 30-50 fs, which becomes increasingly complete with more degrees of freedom included in the calculation. The results are briefly compared with analogous data for the s-trans-butadiene system treated by some of us recently.

Ab initio quantum study of nonadiabatic S(1)-S(2) photodynamics of s-trans-butadiene.

The nonadiabatic photodynamics of s-trans-butadiene in its lowest singlet excited states is studied theoretically, using a fully quantal approach. The coupled 1Bu and 2Ag states are considered in the calculation, representing the lowest dipole-allowed electronic transition, and the dipole-forbidden state with substantial double-excitation character, respectively. Up to six nuclear degrees of freedom, including out-of-plane dihedral angles, are included. The calculation of the underlying potential energy surfaces relies on the CASPT2 method, where widely different CAS spaces have been compared. The ultrafast electronic population decay is confirmed, proceeding on a time scale of 30-40 fs. Pronounced out-of-plane distortions are obtained for the first time from fully quantal calculations. The complexity of the electronic absorption spectrum increases substantially upon including additional vibrational modes in the calculation. Further computations were performed to facilitate inclusion of the coupling to the ground state in subsequent work.

Reaction surface approach to multimode vibronic coupling problems: general framework and application to furan.

A new general framework for treating the dynamics on intersecting multidimensional potential energy surfaces is presented. It rests on a sub-division of the nuclear coordinates into different classes, one of primary importance with large-amplitude displacements during the process of interest and another one with smaller displacements, thus permitting a more approximate description. The latter are treated within the well-known linear + quadratic vibronic coupling scheme, where, however, the expansion "coefficients" are general functions of the "primary" coordinates. This may be augmented by an effective-mode approach for further degrees of freedom acting as an environment for the dynamics of the original modes. Following the general considerations, the approach is applied to the nonadiabatic photodynamics of furan and is shown to allow for an eight-dimensional quantum treatment, of higher dimension than was possible so far. The influence of the various degrees of freedom on the dynamics and lifetime of furan due to nonadiabatic ring-opening is discussed.

Quantum dynamics through conical intersections: combining effective modes and quadratic couplings.

We present a detailed study for the short-time dynamics through conical intersections in molecular systems related to the quadratic vibronic coupling (QVC) Hamiltonian [Müller, H.; Köppel, H.; Cederbaum, L. S. New J. Chem. 1993, 17, 7-29] and the effective-mode formalism [Cederbaum, L. S.; Gindensperger, E.; Burghardt, I. Phys. Rev. Lett. 2005, 94, 113003]. Our approach is based on splitting the nuclear degrees of freedom of the whole system into system modes and environment modes. It was found that only three-effective environmental modes together with the system's modes are needed to describe the short-time dynamics of the complex system correctly. In addition, a detailed mathematical proof is given in the appendix to demonstrate that the exact cumulants are recovered up to the second order within the cumulant expansion of the autocorrelation function. The butatriene molecule is studied as an explicit showcase example to stress the viability of our proposed scheme and to compare with other systems.

Ab initio quantum dynamical study of photoinduced ring opening in furan.

The nonadiabatic photoinduced ring opening occurring in the two lowest excited singlet states of furan is investigated theoretically, using wave-packet propagation techniques. The underlying multidimensional potential energy surfaces (PESs) are obtained from ab initio computations, using the equation-of-motion coupled cluster method restricted to single and double excitations (EOM-CCSD), reported in earlier recent work [E. V. Gromov, A. B. Trofimov, F. Gatti, and H. Köppel, J. Chem. Phys. 133, 164309 (2010)]. Up to five nuclear degrees of freedom are considered in the quantum dynamical treatment. Four of them represent in-plane motion for which the electronic states in question (correlating with the valence (1)B(2)(V) and Rydberg (1)A(2)(3s) states at the C(2v) ground-state molecular configuration) have different symmetries, A(') and A(''), respectively. The fifth mode, representing out-of-plane bending of the oxygen atom against the carbon-atom plane, leads to an interaction of these states, as is crucial for the photoreaction. The nonadiabatic coupling and conical intersection cause an electronic population transfer on the order of ∼10 fs. Its main features, and that of the wave-packet motion, are interpreted in terms of properties of the PES. The lifetime due to the ring-opening process has been estimated to be around 2 ps. The dependence of this estimate on the nuclear degrees of freedom retained in the computations is discussed.

Ab initio quantum dynamical study of the multi-state nonadiabatic photodissociation of pyrrole.

There has been a substantial amount of theoretical investigations on the photodynamics of pyrrole, often relying on surface hopping techniques or, if fully quantal, confining the study to the lowest two or three singlet states. In this study we extend ab initio based quantum dynamical investigations to cover simultaneously the lowest five singlet states, two π-σ∗ and two π-π∗ excited states. The underlying potential energy surfaces are obtained from large-scale MRCI ab initio computations. These are used to extract linear and quadratic vibronic coupling constants employing the corresponding coupling models. For the N-H stretching mode Q(24) an anharmonic treatment is necessary and also adopted. The results reveal a sub-picosecond internal conversion from the S(4) (π-π∗) state, corresponding to the strongly dipole-allowed transition, to the S(1) and S(2) (π-σ∗) states and, hence, to the ground state of pyrrole. The significance of the various vibrational modes and coupling terms is assessed. Results are also presented for the dissociation probabilities on the three lowest electronic states.

Ab initio study of the VUV-induced multistate photodynamics of formaldehyde.

Although formaldehyde, H2CO, has been extensively studied there are still several issues not-well understood, specially regarding its dynamics in the VUV energy range, mainly due to the amount of nonadiabatic effects governing its dynamics. Most of the theoretical work on this molecule has focused on vertical excitation energies of Rydberg and valence states. In contrast to photodissociation processes involving the lowest-lying electronic states below 4.0 eV, there is little known about the photodynamics of the high-lying electronic states of formaldehyde (7-10 eV). One question of particular interest is why the (π, π*) electronic state is invisible experimentally even though it corresponds to a strongly dipole-allowed transition. In this work we present a coupled multisurface 2D photodynamics study of formaldehyde along the CO stretching and the symmetric HCH bending motion, using a quantum time-dependent approach. Potential energy curves along all the vibrational normal modes of formaldehyde have been computed using equation-of-motion coupled cluster including single and double excitations with a quadruply augmented basis set. In the case of the CO stretching coordinate, state-averaged complete active space self-consistent field followed by multireference configuration interaction was used for large values of this coordinate. 2D (for the CO stretching coordinate and the HCH angle) and 3D (including the out-of-plane distortion) potential energy surfaces have been computed for several Rydberg and valence states. Several conical intersections (crossings between potential energy surfaces of the same multiplicity) have been characterized and analyzed and a 2D 5 × 5 diabatic model Hamiltonian has been constructed. Based on this Hamiltonian, electronic absorption spectra, adiabatic and diabatic electronic populations and vibrational densities have been obtained and analyzed. The experimental VUV absorption spectrum in the 7-10 eV energy range is well reproduced, including the vibrational structure and the high irregularity in the regime of strong interaction between the (π, π*) electronic state and neighboring Rydberg states.

Theoretical study of photoinduced ring-opening in furan.

The potential energy surfaces (PESs) of the two lowest excited singlet states of furan [correlating with the Rydberg (1)A(2)(3s) and valence (1)B(2)(V) states at the C(2v) ground-state molecular configuration] have been studied in some detail with regard to the photoinduced ring-opening reaction. The surfaces have been characterized in terms of their stationary points and points of minimum energy conical intersections along the ring-opening pathway. The optimization of the geometrical parameters has been performed with the equation of motion coupled cluster singles and doubles method. The ab initio PESs have been modeled by energy grids and Taylor series. The resulting 11-dimensional PESs reproduce the ab initio results to a good accuracy and can be used in dynamical calculations.

Few-femtosecond passage of conical intersections in the benzene cation.

Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in the femtochemistry toolkit. Such dynamics are now within reach with the instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess the ultrafast nonadiabatic vibronic processes in a prototypical complex system-the excited benzene cation. We use few-femtosecond duration extreme ultraviolet and visible/near-infrared laser pulses to prepare and probe excited cationic states and observe two relaxation timescales of 11 ± 3 fs and 110 ± 20 fs. These are interpreted in terms of population transfer via two sequential conical intersections. The experimental results are quantitatively compared with state-of-the-art multi-configuration time-dependent Hartree calculations showing convincing agreement in the timescales. By characterising one of the fastest internal conversion processes studied to date, we enter an extreme regime of ultrafast molecular dynamics, paving the way to tracking and controlling purely electronic dynamics in complex molecules.

Nongenomic effects of aldosterone on human renal cells.

The development of chronic renal insufficiency may be partially mediated by the nongenomic action of aldosterone. Here we investigate whether aldosterone could evoke a nongenomic action in primary cultures of human renal cells. Intracellular Ca(2+) ([Ca(2+)](i)) and cAMP were measured in human mesangial cells (MC), glomerular visceral epithelial cells (GVEC), and proximal and distal tubular epithelial cells (Ptec and Dtec) in the presence of aldosterone (10-100 nmol/liter) by fura-2 fluorescence and RIA, respectively. In MC, Ptec, and Dtec, aldosterone increased [Ca(2+)](i) within 1 min, whereas in GVEC, only a minor effect was found. Preincubation of cells with spironolactone did not blunt this effect. Hydrocortisone, used at a concentration 100-fold higher than that of aldosterone, did not affect [Ca(2+)](i.) In MC, Ptec, and Dtec, a dose-dependent increase ( approximately 1.3- to 1.5-fold) in intracellular cAMP levels was found. These data demonstrate a nongenomic action of aldosterone in human MC, Ptec, and Dtec. As these effects occur at concentrations close to free plasma aldosterone levels in man, they may be of physiological relevance and may contribute to renal injury.

Endocytosis and autophagy in dying neurons: an ultrastructural study in chick embryos.

In an effort to understand naturally occurring neuronal death in the developing isthmo-optic nucleus, we have accentuated one of its most probably causes, failure to receive adequate trophic maintenance from the axonal terminal zone in the retina, and have studied the dying neurons ultrastructurally. Retrograde trophic maintenance was blocked by means of intraocularly injected colchicine, which caused all the isthmo-optic neurons to die by just one of the two or more kinds of cell death that they undergo during normal development. The present paper deals with the very prominent cytoplasmic aspects of this kind of cell death, notably the uptake of exogeneous horseradish peroxidase and autophagy. There were also nuclear changes, which are dealt with mainly in the accompanying paper (Clarke and Hornung, J. Comp. Neurol. 283:438-449,'89). Numerous cytoplasmic vacuoles occurred in both soma and dendrites, and they were of three main kinds, of which the smallest (less than 0.5 microns diameter) had unstructured contents, whereas the larger two (1-2 microns and 2-7 microns) were secondary lysosomes (mostly residual bodies). Intravascularly injected horseradish peroxidase labeled all three kinds of vacuole but not the free cytoplasm, indicating that the uptake was by endocytosis rather than by leakage through holes in the membrane, as is confirmed by our failure to detect any such holes. We suspect that the smallest vacuoles are the primary endosomes, that these subsequently fuse with vacuoles of the intermediate kind, and that the largest vacuoles are formed by the fusion of these latter. The purpose of the endocytosis may be to channel the plasma membrane piecemeal into the lysosomes for destruction.

Segmental degradation of left ventricular wall motion after persistent coronary fistula in a posttransplantation patient: a case report and short review of literature.

A 50-year-old man received an orthotopic heart transplant because of severe coronary heart disease and congestive heart failure. Two years after the transplantation, a continuous murmur occurred at the left sternal edge after repeated endomyocardial biopsies. Echocardiography and coronary angiography revealed a dilated left anterior descending artery with a fistula to the right ventricle. The circumflex was large with an equally postero-lateral branch, and the right coronary artery was rather small with collaterals to the distal part of the left anterior descending branch. The patient had refused any intervention to close the fistula. The left ventricular levogram was normal. Two years later, in a follow-up angiogram, the left ventricular ejection fraction had decreased as a result of hypo- and akinesis of the apex and posterior wall. We suggest that this local wall motion disturbance derives from a steal phenomenon rather than being a sequela of rejection. The decrease in left ventricular ejection fraction was associated with shortness of breath upon moderate exercise. Standard heart failure medication relieved the patient's symptoms. The observation of local wall motion disturbances in this case, as well as conflicting views in the literature, raises the question whether postbiopsy coronary fistulas in transplant patients should be closed.

Factor II G20210A and factor V G1691A gene mutations and peripheral arterial occlusive disease.

BACKGROUND: G to A mutations at positions 20210 of the prothrombin gene (F2) and 1691 of the factor V gene (F5) are established risk factors for venous thrombosis. Several factors associated with coagulation and/or fibrinolysis have been associated with arterial occlusive disease, but the role of F2 20210A and F5 1691A for arterial occlusive disease remains unclear. OBJECTIVE: To investigate if F2 20210A and F5 1691A are associated with peripheral arterial occlusive disease (PAOD). METHODS AND RESULTS: We analyzed the prevalence of F2 20210A and F5 1691A alleles in 336 patients with documented PAOD at Fontaine stage II-IV and 300 controls without vascular disease. Allele frequencies in patients and controls were 0.013 and 0.022 for F2 20210A, and 0.042 and 0.045 for F5 1691, respectively, both differences being not statistically significant. CONCLUSION: Our data suggest that mutations F2 G20210A and F5 G1691A are not associated with PAOD.

Inhibition of vascular K(ATP) channels by U-37883A: a comparison with cardiac and skeletal muscle.

1 The aim of this study was to investigate the selectivity of the ATP-sensitive potassium (K(ATP)) channel inhibitor U-37883A (4-morpholinecarboximidine-N-1-adamantyl-N'-1-cyclohexyl). Membrane currents through K(ATP) channels were recorded in single muscle cells enzymatically isolated from rat mesenteric artery, cardiac ventricle and skeletal muscle (flexor digitorum brevis). K(ATP) currents were induced either by cell dialysis with 0.1 mM ATP and 0.1 mM ADP, or by application of synthetic potassium channel openers (levcromakalim or pinacidil). 2 U-37883A inhibited K(ATP) currents in smooth muscle cells from rat mesenteric artery. Half inhibition of 10 microM levcromakalim-induced currents occurred at a concentration of 3.5 microM. 3 Relaxations of rat mesenteric vessels caused by levcromakalim were reversed by U-37883A. 1 microM levcromakalim-induced relaxations were inhibited at a similar concentration of U-37883A (half inhibition, 1.1 microM) to levcromakalim-induced KATP currents. 4 K(ATP) currents activated by 100 microM pinacidil were also studied in single myocytes from rat mesenteric artery, skeletal muscle and cardiac ventricle. 10 microM U-37883A substantially inhibited K(ATP) currents in vascular cells, but had little effect in skeletal or cardiac myocytes. Higher concentrations of U-37883A (100 microM) caused a modest decrease in K(ATP) currents in skeletal and cardiac muscle. The sulphonylurea K(ATP) channel antagonist glibenclamide (10 microM) abolished currents in all muscle types. 5 The effect of U-37883A on vascular inward rectifier (KIR) and voltage-dependent potassium (KV) currents was also examined. While 10 microM U-37883A had little effect on these currents, some inhibition was apparent at higher concentrations (100 microM) of the compound. 6 We conclude that U-37883A inhibits K(ATP) channels in arterial smooth muscle more effectively than in cardiac and skeletal muscle. Furthermore, this compound is selective for K(ATP) channels over KV and KIR channels in smooth muscle cells.

Isolation and characterisation of proliferating cells from the telencephalic vesicles of gestational-day 13 rats.

A method of isolating in culture a specific subpopulation of cells in the "S" phase of the mitotic cycle, from embryonic forebrain, is described. Different enzyme treatment and different substratum pretreatment are compared quantitatively to ensure optimal yield. These cells, isolated from the telencephalic vesicles of embryonic day (E) 13 rat embryos, were maintained in culture and their morphological and immunocytochemical characteristics were investigated at one and eight days in vitro.

Transitory macrophages in the white matter of the developing visual cortex. I. Light and electron microscopic characteristics and distribution.

Injections of horseradish peroxidase (HRP) into the occipital cortex of the kitten and diffusing to the white matter label a widely distributed microglial population and in addition, cells with light and electron microscopic features of 'gitter cells'. The latter are concentrated in a complex and highly consistent system of interconnected clusters in the white matter of the lateral, postlateral, middle suprasylvian and posterior ectosylvian gyri, as well as on the roof of the lateral ventricle. The 'gitter cells' have the ultrastructural and (as described by others) chemical characteristics of macrophages, and may be involved in the elimination of transitory axons.

Transitory macrophages in the white matter of the developing visual cortex. II. Development and relations with axonal pathways.

Clusters of 'gitter cells' develop in the white matter of the occipital cortex of the cat at the end of the first postnatal week. These clusters, and others already present at birth, disappear by the end of the first postnatal month. The life span of the clusters in the occipital white matter corresponds to the period when transitory callosal axons are eliminated. The clusters have close contact with callosal axons and can be labeled by HRP injected in the contralateral hemisphere and transported through the corpus callosum. One of the clusters clearly forms in a part of the white matter crossed by transitory callosal axons. The 'gitter cells' might be involved in the elimination of these axons. Consistent with this hypothesis, ultrastructural observations show groups of axons completely surrounded by 'gitter cell' cytoplasm as if they were being phagocytosed.