Optical Properties of Mass Selected Clusters

The TOF spectrum of the mass selected Sr+Ar3 cluster after the photofragmentation with a tunable OPO laser at =450 nm.

The study of metal-ion noble gas/molecule complexes aims to improve our understanding of the nature of interaction forces responsible for molecular bonding. The development of novel cluster ion sources based on laser ablation of metal targets, in combination with photofragmentation spectroscopy of mass selected ions, offers a direct way for studying the optical properties (absorption spectra) of an ionic complex of interest.

The Technique

From the size distribution of the clusters M+Xn (n=1 to tens, hundreds) produced from the ion source, a particular ion M+Xn is mass-selected with the mass-gate. After the mass-gate, a light beam from a tunable laser intersects the ion beam and causes photofragmentation. Because of the conservation of energy, the fragments have lower kinetic energy than the parents, penetrate less deep into the reflectron and arrive earlier at the detector being separated from the parent masses in the TOF spectrum. The photofragmentation spectrum is obtained by normalising the total intensity of ions by the intensity of the parent and the laser intensity ILaser at each different laser frequency. Assuming single photon absorption and that each absorbed photon leads at least to one evaporation event in the time window of measurement (~10sec), the photofragmentation cross section is equal or constitutes a lower limit for the photoabsorption cross section.

References:

 

Ch. Lüder, D. Prekas, A. Vourliotaki, and M. Velegrakis, Photodissociation spectrum of Sr+Ne, Chem. Phys. Lett. 267, 149 (1997)

 

Flowchart: Alternate Process: Photofragmentation spectrum of Sr+Ne

D0=630 cm-1

e=105

 

D0=104 cm-1

e=20

 

Down Arrow:

Potential parameters

Binding energy

Vibrational frequency

Anharmonicity,

etc.