C. Callegari

Helium nanodroplet isolation rovibrational spectroscopy: Methods and recent results

In this article, recent developments in helium nanodroplet isolation (HENDI) spectroscopy are reviewed, with an emphasis on the infrared region of the spectrum. We discuss how molecular beam spectroscopy and matrix isolation spectroscopy can be usefully combined into a method that provides a unique tool to tackle physical and chemical problems which had been outside our experimental possibilities. Next, in reviewing the experimental methodology, we present design criteria for droplet beam formation and its seeding with the chromophore(s) of interest, followed by a discussion of the merits and shortcomings of radiation sources currently used in this type of spectroscopy. In a second, more conceptual part of the review, we discuss several HENDI issues which are understood by the community to a varied level of depth and precision. In this context, we show first how a superfluid helium cluster adopts the symmetry of the molecule or complex seeded in it and discuss the nature of the potential well (and its ani...

The FERMI@Elettra free-electron-laser source for coherent X-ray physics: photon properties, beam transport system, and applications

FERMI@Elettra is comprised of two free electron lasers (FELs) that will generate short pulses (tau ~;; 25 to 200 fs) of highly coherent radiation in the XUV and soft X-ray region. The use of external laser seeding together with a harmonic upshift scheme to obtain short wavelengths will give FERMI@Elettra the capability to produce high quality, longitudinal coherent photon pulses. This capability together with the possibilities of temporal synchronization to external lasers and control of the output photon polarization will open new experimental opportunities not possible with currently available FELs. Here we report on the predicted radiation coherence properties and important configuration details of the photon beam transport system. We discuss the several experimental stations that will be available during initial operations in 2011, and we give a scientific perspective on possible experiments that can exploit the critical parameters of this new light source.

Photoinduced Chemical Dynamics of High-Spin Alkali Trimers

Nanometer-sized helium droplets, each containing about 104 helium atoms, were used as an inert substrate on which to form previously unobserved, spin-3/2 (quartet state) alkali trimers. Dispersed fluorescence measurements reveal that, upon electronic excitation, the quartet trimers undergo intersystem crossing to the doublet manifold, followed by dissociation of the doublet trimer into an atom and a covalently bound singlet dimer. As shown by this work, aggregates of spin-polarized alkali metals represent ideal species for the optical study of fundamental chemical dynamics processes including nonadiabatic spin conversion, change of bonding nature, and unimolecular dissociation.

Superfluid Hydrodynamic Model for the Enhanced Moments of Inertia of Molecules in Liquid 4 He

We present a superfluid hydrodynamic model for the increase in moment of inertia,

Finite size effects and rotational relaxation in superfluid helium nanodroplets: Microwave-infrared double-resonance spectroscopy of cyanoacetylene

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First overtone helium nanodroplet isolation spectroscopy of molecules bearing the acetylenic CH chromophore

, of molecules rotating in liquid

Microwave spectra of HCN and DCN in 4He nanodroplets: A test of adiabatic following

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Coherent control with a short-wavelength free-electron laser

He. The static inhomogeneous He density around each molecule (calculated using the Orsay-Paris liquid

Alkali–helium exciplex formation on the surface of helium nanodroplets. I. Dispersed emission spectroscopy

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Single and Double Resonance Microwave Spectroscopy in Superfluid 4 He Clusters

He density functional) is assumed to adiabatically follow the rotation of the molecule. We find that the