On the photoionization and fragmentation of ammonia clusters using TPEPICO

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The photoionisation threshold region of homogeneous Argon and Krypton clusters Ar, and Kr, for n up to 24 formed in a free jet expansion has been studied in detail, using the threshold photoelectron photoion coincidence (TPEPICO) time of flight technique. Measurements performed at a variety of different expansion conditions (nozzle temperature and stagnation pressure) demonstrate that fragmentation of larger clusters contributes substantially to the shape of the TPEPICO spectra even for the smallest clusters and at all photon energies higher than about 200 meV to 400 meV above the ionisation threshold. The determination of ionisation potentials for these cluster ions is discussed and careful estimates are given and compared with recent theoretical values.

Section: Methodsmentioning

confidence: 99%

“…demonstrated in our measurements on (N20), [52] and (NH3) . clusters [48]. For the rare gases, however, the photon energy range over which fragmentation cannot contribute is rather small, due to the very small binding energy of the neutral clusters.…”

Section: Fragmentationmentioning

confidence: 98%

Photoionisation studies of homogeneous argon and krypton clusters using TPEPICO

Kamke

Vries

Krauss

et al. 1989

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“…7. To derive this diagram we have used the experimental and theoretical data available from the literature for the neutral cluster binding energies D,_ 1,~ (theory from Greer et al [1]), the binding energies D~_ 1,n of NH3 to the protonated ion NH~-(NH3),_ 2 from thermochemical data [3], the appearance potentials for (NH3), + and NH2 + NH~(NH3)n_ 2 from the single photon ionisation studies by Kamke et al [7] and the recently determined photoionisation energy of the long lived neutral NH4(NH3), complexes [17]. The electronic excitation energies of the states corresponding to the/] state of NH3 can only be estimated.…”

Section: Energeticsmentioning

confidence: 99%

“…if the ionisation is soft and not too much excess energy is deposited into the system [7]. Stable homogeneous cluster ions (NH3)~ + can be formed e.g.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast fragmentation and ionisation dynamics of ammonia clusters

Freudenberg

Radloff

Ritze

et al. 1996

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Abstract.The formation ofprotonated and unprotonated ammonia cluster ions is studied by femtosecond two colour two photon pump-probe techniques applied to (NH3), and (ND3), clusters with n up to 8. The fourth harmonic ( ~ 200 nm, 6.2 eV, 160 fs) of a Ti : Sapphire laser pulse is used to excite the clusters in a state corresponding to the A state of NH3 while the third harmonic (267 nm, 4.65 eV) is used for the subsequent ionisation step. Employing a combination of the optical Bloch equations for the excitation process and rate equations for the cluster dynamics we calibrate the zero time delay and carefully analyse the time dependence of the pump-probe signal. Several distinct intermediate steps in the time evolution can be distinguished, having characteristic time constants ranging from 40 fs to over 100 ps. They are discussed in a consistent scheme for the excitation, ionisation and protonation dynamics, accounting also for characteristic differences observed between deuterated and undeuterated species. A particularly remarkable time dependence of the homogeneous (NH3)f cluster ion signal is interpreted as a fingerprint of internally protonated neutral precursors of the type NH3NH2NH4.

“…For pure (NH3), clusters the threshold for protonated ions is much higher (e.g. 8.8 eV at n = 7 [17]) than the photon energy of 5.4 eV in our experiment. The lower ionization potentials of Ag(NH3), alone cannot explain theses differences.…”

Section: Protonated Cluster Ionsmentioning

confidence: 74%

Laser ionization spectroscopy of Ag(NH3) n clusters

Freudenberg

Radloff

Ritze

et al. 1995

Abstract. The ionization and the fragmentation properties of Ag(NH3), heteroclusters have been studied. The measured ion yield spectra near the threshold for complexes with n = 2-20 indicate strong differences of the cluster geometry in the electronic ground and in the ionized state, respectively. For smaller clusters (n _< 6) in the neutral ground state the nonsolvated Ag atom is localized near the surface of the complex. A modification of the surface structure at the transition to larger clusters (n > 7) is suggested by significant changes in the ionization and fragmentation behaviour. Preliminary results of ab initio calculations confirm the conclusion that due to the correlation interaction between the valence electron and the 4d electrons of the Ag atom no solvation effects occur.