Stabilities of protonated water-ammonia clusters

Branching ratios of water and ammonia evaporation have been measured for spontaneous evaporation from protonated mixed clusters H + (H 2 O) n (NH 3 ) m in the size range 0 ≤ n ≤ 11 and 0 ≤ m ≤ 7. Mixed clusters evaporate water except for clusters containing six or more ammonia molecules, indicating the formation of a stable core of one ammonium ion surrounded by four ammonia molecules and a second shell consisting predominantly of water. We relate evaporative branching ratios to free energy differences between the products of competing channels and determine the free energy differences for clusters with up to seven ammonia molecules. Clusters containing up to five ammonia molecules show a very strong scaling of these free energy differences

Cooling dynamics of carbon cluster anions

A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for Cn- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account

Non-scrambling of hydrogen in NH4+(H2O)3 clusters

We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, dn-NH4+(H2O)3, n = 0-6. The mass spectra show a very strong odd-even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium-deuterium water molecule intermediate between these two values

Thermal properties of clusters and molecules - Experiments on evaporation, thermionic emission, and radiative cooling

This thesis presents experiments performed on clusters and molecules, where the three channels of unimolecular decay have been studied. Evaporation from protonated and negatively charged water cluster have yielded size dependent heat capacities, where the smallest sizes with fewer than $21$ molecules show a heat capacity similar to bulk ice whereas clusters with molecules between $21$ and $300$ have a heat capacity in between that of ice and liquid water. The increase in heat capacity per added molecule in the cluster indicates that the intramolecular degrees of freedom are frozen at the temperatures in the experiment (T$\approx\!\!\!160$~K). Experiments on small mixed water-ammonia clusters resulted in relative evaporation fractions for sizes between a total of three to eleven molecules, and $16$ molecules. The clusters were found to evaporate predominantly water molecules except for clusters containing six or more ammonia molecules. Relative evaporation rates for D$_2$O, HDO, and H$_2$O were measured for NH$_4^+$(H$_2$O)$_4$ with zero to six deuteriums interchanged with the hydrogens. The relative rates were found to be $1:0.71:0.56$. Absolute timedependent cooling rates for hot C$_{60}^-$ were obtained in an electrostatic storage ring with single photon absorption experiment. The cooling of the molecule could be divided into a thermionic emission part and a radiative part, where the crossover between the two occurred at $5$~ms, after which radiation was shown to be the dominant cooling channel. The spontaneous decay profiles were used to extract decay parameters of the large organic anion zink phthalocyanine (ZnPc). Numerical simulations of the decay process show good agreement with measurements, using parameters derived from an analytical approximation also used for fullerenes. Photoabsorption experiments were performed on the much smaller C$_5^-$, showing the presence of strong radiative cooling. The cooling rate was determined by the dependence of the photoinduced neutralization yield vs. photon energy and laser firing time

Radiative cooling of C7-

The spontaneous and photo-induced neutralization of C_7- produced in a laser ablation source was measured in an electrostatic storage ring. The measurements provide three independent determinations of the radiative cooling of the ions, based on the short time spontaneous decay and on the integrated amplitude and the shape of the photo-induced neutralization signal. The amplitudeof the photo-induced signal was measured between 0.5 ms and 35 ms and found to depend on photon wavelength and ion storage time. All three signals can be reproduced with identical thermal IR radiative cooling rates with oscillator strengths equal to theoretical predictions. In addition,the measurements provide the excitation energy distribution

Inverse internal conversion in C 4 - below the electron detachment threshold

Inverse internal conversion followed by recurrent fluorescence was observed as a fast decay (10 μs range) in the time profile of neutral yields from photo-excited C4- molecular ions. We also elucidated the contribution of such electronic radiative cooling to the C4- ions with internal energy far below the detachment threshold by an alternative novel approach, observing the laser wavelength and storage time dependence (ms range) of the total yield of the photo-induced neutrals