Narda Ben‐Horin

Electronic spectral shifts of aromatic molecule-rare-gas heteroclusters

In this paper, a semiempirical theory for the spectral shifts of the electronic origin of the S0→S1 transition of (aromatic molecule)⋅(rare‐gas)n heteroclusters is advanced and applied. Neglecting the modifications of intermolecular overlap and exchange interactions upon electronic excitation, the dispersive contributions to the spectral shift are evaluated to second order, accounting for finite‐size structural features of the large molecule by the utilization of the multicenter monopole representation of the intermolecular interactions. The spectral shifts for nonpolar aromatic hydrocarbons in or on rare‐gas heteroclusters are represented in terms of differences between electrostatic interactions involving an electrostatic field (due to the molecular transition monopoles charge distribution) and an induced dipole (originating from the rare‐gas polarizability). The transition monopoles incorporated all the one‐ and two‐electron ππ* excitations of the aromatic molecule, which were represented by Huckel or ...

Spectroscopy and nuclear dynamics of tetracene–rare‐gas heteroclusters

In this paper we report on the electronic spectroscopy of mass‐resolved tetracene⋅Arn (n=1–26) and tetracene⋅Krn (n=1–14) heteroclusters, utilizing two‐photon, two‐color near‐threshold ionization in conjunction with mass‐spectrometric detection. The spectra of the S0 → S1 transition and the ionization threshold of these heteroclusters were monitored. The structured spectral features of the S0 → S1 transition of small‐ and medium‐sized (n=1–8) heteroclusters were attributed to the electronic origins of structural isomers and to their intermolecular vibrations. The S0 → S1 spectra of large (n≥9) heteroclusters are broad and were assigned to inhomogeneous broadening due to the coexistence of isomers, with the spectral feature(s) of each distinct isomer being homogeneously broadened. Isomer‐specific inhomogeneous line broadening was interrogated by the observation of isomer‐specific ionization potentials for medium‐sized (n=6–7) heteroclusters and of the dependence of the relative intensities of the spectral ...

Rigid and nonrigid benzene·Ar2 van der Waals heteroclusters

Abstract The nonrigidity of the one-sided (2|0) isomer of benzene·Ar 2 is manifested by the occurrence of a hierarchy of distinct isomerization processes and by the marked broadening of the photoionization efficiency curves, which were explored by constant energy molecular dynamics simulations.

Hierarchical isomerization of molecular clusters

Abstract Electronic spectra of mass-specific dichloroanthracene. Ar N ( N = 1−55) and dichloroanthracene Kr N ( N = 1−20) clusters were interrogated by resonant two-photon two-color ionization, providing information on multistate isomerization phenomena which involve coexistence of isomers, wetting-nonwetting transitions, solvation shell closure and nonrigid-rigid transitions. A novel effect of spectral line narrowing with increasing cluster size is observed for the nonrigid-rigid transition in doped heteroclusters.

Spectroscopic cluster size effects

In this paper we examine the spectral moments of the absorption line shapes of aromatic‐ molecule⋅(rare gas)n heteroclusters to provide analytic expressions for the spectral shifts (δν), which are determined by the first moment, and for the homogeneous linewidths (Γ), which are determined by the central second moment (Δ) of the line shape. δν originates from the cumulative contributions of dispersive pair interactions, while Δ and Γ manifest the short‐range dynamic nuclear fluctuations. Our analysis elucidates some of the general features of these spectroscopic observables, e.g., their dependence on the cluster structure and their size dependence, as well as some of their specific characteristics, e.g., their temperature dependence. We predict a weak temperature dependence of δν (=a+bT with b≪a/T) and a strong temperature dependence of Δ(∝T1/2), which is borne out by molecular dynamics (MD) simulations. We have derived cluster size equations (CSE) relating the spectroscopic observables of the finite clust...

Radiative lifetimes of van der Waals heteroclusters

In this paper we advance and apply a molecular theory of pure radiative lifetimes τr of (aromatic molecule)⋅(rare gas)n heteroclusters. The modification of τr in the heterocluster, relative to the bare molecule value, originates from intermolecular interactions between molecular multicenter transition monopoles, which are described by π electron approximation, and the rare‐gas atom transition dipoles, which are specified in terms of the static atomic polarizability α. The calculated changes of τr of 9,10 dichloroanthracene⋅A1 (A=Ar, Kr, Xe) heterodimers are in good agreement with experiment; the theory accounting for the nearly linear dependence of the change of τr on α.Calculations of the radiative lifetimes of 9,10 dichloroanthracene⋅Arn (n=1–34) heteroclusters were performed using structural information from potential optimization for small (n=1–3) heteroclusters, static structural data for small and medium‐sized (n=1–8) heteroclusters, and (constant energy) finite‐temperature molecular dynamics simula...

Spectroscopic interrogation of heterocluster isomerization. I. Simulations of nuclear dynamics and electronic spectroscopy

In this paper we explore the structure, energetics, nuclear dynamics, isomerization, and electronic‐vibrational spectroscopy of large finite systems by constant energy molecular dynamics (MD) simulations of heteroclusters of 9,10‐dichloroanthracene (DCA) with rare‐gas atoms, i.e., DCA⋅Arn (n=1–34) and DCA⋅Krn (n=1–18). We consider the spectroscopic implications of heterocluster size effects, isomer‐specificity, nuclear dynamics, and isomerization as manifested by the spectral shifts (δν) and homogeneous linewidths (Δ) for the S0→S1 transition, the ionization potential shifts (δI) from S0, and the shifts (Δτr) of the pure radiative lifetimes of S1 for these heteroclusters, with δν, δI, and Δτr being given relative to the corresponding observable for the bare DCA molecule. MD simulations of the energetics, rigid and nonrigid structures, fluctuations in structural parameters, and transport properties over a broad temperature region (8–70 K) allowed for the identification of several isomerization phenomena, i...

Perylene–rare‐gas heteroclusters. I. Electronic spectroscopy

In this paper we report on the electronic two‐photon two‐color near threshold spectroscopy of mass‐resolved perylene⋅Arn (n=1–45), perylene⋅Krn (n=1–35), perylene⋅(N2)n (n=1–12), and perylene⋅(CH4)n (n=1–10) heteroclusters. The S0→S1 inhomogeneously broadened spectra of perylene⋅Arn (n=1–6) and perylene⋅Krn (n=1–4) exhibit resolved spectral features, which were assigned on the basis of experimental combination rules and polarizability relations to the electronic origins of distinct two‐sided and one‐sided structural isomers. Larger perylene⋅An (A=Ar, Kr; n=6–10) heteroclusters exhibit an ‘‘abnormal’’ specific size dependence of the red spectral shifts, which decrease with increasing n and reach a local minimum at n=8. Similar characteristics of the red spectral shifts are exhibited for perylene⋅(N2)n and perylene⋅(CH4)n (n=4–8) heteroclusters. This abnormal size dependence of the spectral shifts is attributed to the dominance of one‐sided single‐layered and double‐layered structural isomers in this cluste...

Microscopic and macroscopic solvation of aromatic molecules in aliphatic hydrocarbons

Abstract The S 0 →S 1 transition of heteroclusters of anthracene and tetracene with alkanes was interrogated by resonant two-colour two- photon ionization. The microscopic spectral shifts of tetracene·heptane n ( n =1–12) clusters converge for n >7 to those of the tetracene—heptane solution spectra, documenting a spectroscopic manifestation of the gradual “transition” from finite to infinite systems.

Microscopic spectral shifts of large van der waals heteroclusters

Abstract Microscopic spectral shifts of the electronic spectra of heteroclusters consisting of inert-gas atoms bound to a large aromatic molecule were evaluated utilizing the multicentre monopole representation for the dispersive intermolecular interactions, which rests on the Huckel of SCF π molecular wavefunctions, in conjunction with a semi-empirical scaling of the transition monopoles. A successful application of this semi-empirical scheme for the evaluation of the spectral shifts of tetracene·R n (R=Ar,Kr) clusters with n =1–6 correlates structural and spectroscopic data.