Infrared photochemistry of ethylene clusters

Infrared irradiation of ethylene clusters formed in supersonic molecular beams, using a low power cw CO2 laser, results in the photodissociation of a large fraction of the van der Waals molecules. Under such conditions, infrared absorption intensity exhibits first-order power dependence and is readily detected as loss in molecular beam intensity. Intramolecular energy transfer rates, determined by measuring spectral linewidths, are shown to vary with the vibrational mode initially excited. Ethylene clusters containing one quantum of vibrational energy corresponding to the nun7 fundamental in the monomer (949 cm^–1) have a vibrationally predissociative lifetime of 0.33 psec. In comparison, the relaxation rate of ethylene-d4 clusters with one quantum of excitation corresponding to the nu12 (1078 cm^–1) mode of C2D4 is 0.7 psec

A theoretical simulation of the resonant Raman spectroscopy of the H2O⋯Cl2 and H2O⋯Br2 halogen-bonded complexes

The resonant Raman spectra of the H2O⋯Cl2 and H2O⋯Br2 halogen-bonded complexes have been studied in the framework of a 2-dimensional model previously used in the simulation of their UV-visible absorption spectra using time-dependent techniques. In addition to the vibrational progression along the dihalogen mode, a progression is observed along the intermolecular mode and its combination with the intramolecular one. The relative intensity of the inter to intramolecular vibrational progressions is about 15% for H2O⋯Cl2 and 33% for H2O⋯Br2. These results make resonant Raman spectra a potential tool for detecting the presence of halogen bonded complexes in condensed phase media such as clathrates and ice.Fil: Franklin Mergarejo, Ricardo. Université Paris Sud; Francia. Centre National de la Recherche Scientifique; Francia. InSTEC; Cuba. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rubayo Soneira, Jesús. InSTEC; CubaFil: Halberstadt, Nadine. Université Paris Sud; Francia. Centre National de la Recherche Scientifique; FranciaFil: Janda, Kenneth C.. University of California at Irvine; Estados UnidosFil: Apkarian, V. Ara. University of California at Irvine; Estados Unido

Bakeout controller for the use of helium closed-cycle refrigerators in ultrahigh vacuum applications

imple control electronics are described which provide automated bakeout of an ultrahigh vacuum (UHV) chamber equipped with a helium closed-cycle refrigerator. By preventing the refrigerator from reaching elevated temperatures (T>50 °C) during bakeout, these devices can be utilized in the ultrahigh vacuum environment

Why Parties Narrow their Representative Profile: Evidence from Six European Democracies

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this recordIn this paper, we analyse the conditions under which political parties narrow their representative profile (defined by the scope of the issues or the constituencies they represent). This strategy has been neglected in the party literature, which is mainly focused on the adoption of catch-all strategies among mainstream parties or the tendency to stick to core issues among niche parties. In this paper, we develop a theoretical framework that includes central external and internal drivers of party change and we empirically test this framework using novel survey data covering 121 parties across six European democracies: The United Kingdom, Norway, Germany, Switzerland, Italy and Ireland.European Commissio

Vibrational predissociation of ArCI2: Toward the determination of the potential energy surface of the B state

Accurate quantum mechanical calculations are carried out to test the sensitivity of the spectroscopy and dynamics of the B state of ArCl2 to the steepness of the Morse term, α, of an atom-atom potential. It is discovered that the predissociation dynamics for this molecule are very complicated even in the Δν = -1 regime due to resonances in the continuum manifold of states. In both the Δν = -1 regime and the Δν = -2 regime the rate of vibrational predissociation and the product rotational distribution are extremely sensitive to the value chosen for α, but not in a regular way. For the Δν = -2 regime the variations can be attributed to spacings between resonances and the overlaps of the bright state wave functions with nearby dark states as expected from the intramolecular vibrational relaxation model. In the Δν = -1 regime, the variations are shown to originate from resonances in the ν - 1 continuum set of states. Although this makes it difficult to determine the value for α, a value of 1.8 Å-1 is probably close to the true value. The most useful new data to determine the potential would be measurements of the lifetimes for as many vibrational levels as possible and rotational distributions for excitation to low vibrational levels of the B state. © 1996 American Institute of Physics.This work was supported by the United States National Science Foundation CHE-9423504. In addition, K.C.J. and N.H. wish to acknowledge the joint NSF-CNRS collaboration program for the support of international travel that made this work possible.Peer Reviewe

Vibrational predissociation of the Ar⋯Cl2 van der Waals complex: The small molecule limit for intramolecular vibrational redistribution

A converged three-dimensional quantum treatment of vibrational predissociation in the Ar⋯Cl2(B 3Π0u+;,v′) van der Waals complex is presented. The potential energy surface used is a sum of pairwise Morse atom-atom interactions adjusted asymptotically to a C 6/R6 + C8/R8 anisotropic van der Waals form. Calculations have been performed in the energy region of Ar⋯Cl2(B1v′ = 6, 10, and 11) excited levels. In agreement with the experimental findings, the final rotational distribution of Cl2 is found to be strongly dependent on the initial v′ state being excited, as well as on the number of vibrational quanta lost in the vibrational predissociation process. The role of intramolecular vibrational redistribution for v′ = 10 and 11 for which the Δv= -1 channel is closed is also studied. It is found that the vibrational predissociation (VP) dynamics are dominated by the coupling of the zero-order >bright> state with a single >dark> state from the v′ -1 manifold of van der Waals vibrationally excited states which then decays to the continuum, and that the product state distribution is determined by the dissociation of the dark state. This is characteristic of the sparse limit for intramolecular vibrational redistribution. It also implies that the dissociation rate is not governed by a simple function of the initial quantum numbers such as the one given by the energy gap law. The golden rule approximation gives surprisingly accurate results for Ar⋯Cl2 dynamics. This will be very useful for fitting a potential energy surface to experimental results. © 1992 American Institute of Physics.O. R. would like to acknowledge support from the DGICYT of the Ministerio de Educacion y Ciencia that enabled his stay in Pittsburgh; and K. C. J. would like to acknowledge support from the NSF.Peer Reviewe

From the sparse to the statistical limit of intramolecular vibrational redistribution in vibrational predissociation: ArCl2 as an example

The dynamics of intramolecular vibrational relaxation (IVR) for ArCl2 are examined for a wide range of vibrational and rotational excitation. In order to describe the IVR more efficiently, and characterize it more quantitatively, we propose a refinement of the traditional Bixon-Jortner description in which the active states are prediagonalized to simplify the coupling scheme that must be considered. This allows for an explicit determination of the average density of states and average coupling strength for each initial excitation. We find that the IVR dynamics proceed from the sparse regime for v = 11, for which the first open dissociation channel corresponds to the loss of two Cl2 quanta, to the intermediate-dense regime for v = 25 which dissociates by the loss of 4 quanta. We find that over this range the increase in the density of states is less important than the increase in the coupling strength. For v = 18 we examine the effect of rotation in considerable detail. Initial states that couple via a manifold of 6000 channels can be considered since the calculation is performed on a parallel computer. The effect of increasing J, the total angular momentum excitation, is found to be less than that of increasing K, the degree of rotation about the van der Waals bond. This means that the main effect is not simply an increase of the available density of states due to Coriolis coupling. Understanding the details of IVR in a relatively simple system like ArCl2 should help us understand the dynamics of more complicated molecules. In particular, the case of ArI2 is discussed. © 1997 American Institute of Physics.N.H. thanks the French-Spanish collaboration fund ‘‘Action Integree Picasso’’ (AI96022) for a visit to Spain. This work has been supported by DGICYT (Spain) under Grant No. PB95-0071. We also want to acknowledge DGICYT and CIEMAT, for the use of a CRAYJ90, and CNRS, for the use of the parallel computing facilities (CRAY T3D) at IDRIS.Peer Reviewe

NeCl2 and ArCl2: transition from direct vibrational predissociation to intramolecular vibrational relaxation and electronic nonadiabatic effects†

10 pags. ; 7 figs. This article is part of the A: Benoit Soep Festschrift special issue.Pump−probe results are reported for NeCl2 excited to the Cl2 B state, undergoing vibrational predissociation, and then probed via E ← B transitions. Intensities, lifetimes and product vibrational branching ratios are reported for 16 ≤ v′ ≤ 19 Cl2 stretching quanta. The intensity of the signal rapidly decreases above v′ = 17. Detailed wave packet calculations of the vibrational predissociation dynamics are performed to determine if the experimental results can be explained by the onset of IVR dynamics. The calculations and the experiment are in close accord for low vibrational levels. For higher levels, some, but not all, of the loss of experimental signal can be attributed to IVR. To test whether electronic relaxation dynamics are important for NeCl2 and ArCl2, excited state potential surfaces that incorporate spin orbit coupling effects are calculated. These surfaces are then used in a wave packet calculation that includes both vibrational predissociation and electronic predissociation dynamics. The results show that electronic predissociation is important for ArCl2 levels above v′ = 12. For NeCl2 the calculation suggests that the onset of electronic predissociation should occur for levels as low as v′ = 13 but may not contribute markedly to the observed loss of signal above v′ = 17. Suggestions are made for further studies of this puzzling problem.Acknowledgment. This work has been supported by the US National Science Foundation Grant CHE-0404743, NSFCONACYT J110.385 and the Ministerio de Ciencia e Innovación under projects CTQ2007-62898. R.H. and K.C.J. also acknowledge the UC-MEXUS program for aiding this collaboration.Peer reviewe