Time-Resolved Dynamics of Thermal Isomerization in Cesium-Halide Cluster Anions

Abstract

We have performed time-resolved studies of the dynamics of thermal isomerization occurring in certain cesium-halide cluster anions. Using a pump-probe technique, we have observed the repopulation of a photodepleted isomer within an ensemble as a function of time by monitoring the photoelectron spectrum. The rates of isomerization increase and the isomer lifetimes decrease as functions of temperature. The clusters undergo a gradual phase transition from solid-like to liquid-like states with liquid-like behavior obtained at approximately 500 K, much lower than the bulk melting temperatures of approximately 900 K.

Probing isomer interconversion in anionic water clusters using an Ar-mediated pump-probe approach: Combining vibrational predissociation and velocity-map photoelectron imaging spectroscopies

“…[1][2][3][4] Several reports from our group [5][6][7] have used isomer-selective vibrational spectroscopies 8,9 to trace the major structural difference between isomers I and II at small sizes ͑n ഛ 8͒ to their local electron-binding motifs. Because several distinct structural arrangements of the water cluster anions are generally produced in typical ion sources, they are excellent model systems for understanding the molecular-level mechanics of how an excess electron is accommodated by well-characterized H-bonding networks.…”

Experimental observation of structural phase transition in CsBr clusters

“…Besides specific cluster size effects on the transition size, thermal isomerization has been observed for small anionic CsX clusters (X = Cl, Br, or I) using photoelectron spectroscopy [13,14]. It was reported that at low temperatures cubiclike structures are most abundant while higher temperatures yield also ringlike isomers.…”

Clusters of Ionic Materials

“…For this reason, this evaporation energy can be called vertical, although it includes some structural relaxation. The calculated vertical evaporation energies as a funtion of n yielded abrupt minima for sizes n = 5, 9,12,14,17,20,23,26,28. Evaporation of an MgO molecule from these clusters is relatively easier than from clusters of neighbor sizes.…”

“…The method of gas aggregation from material evaporated in an oven can also be used to produce the clusters. A mass spectrum of (CsI) n Cs + clusters shows that the intensity peak corresponding to (CsI) 13 Cs + , that is [Cs 14 I 13 ] + , is very strong [2], and analogous studies of NaCl and CuBr clusters show that [Na 14 Cl 13 ] + and [Cu 14 Br 13 ] + also have enhanced abundances [3,4]. Figure 10.1.…”

“…Time resolved studies of the thermal isomerization have also been performed [14]. Figure 10.7 shows some photoelectron spectra of one of the isomers (the isomer corresponding to the left peak).…”