Sodium Microsolvation in Ethanol: Common Features of Na(HO-R)_n (R = H, CH₃, C₂H₅) Clusters

Abstract

Ethanol clusters are generated in a continuous He seeded supersonic expansion and doped with sodium atoms in a pick-up cell. By this method clusters of the type Na(C(2)H(5)OH)(n) are formed and characterized by determining size selectively their ionization potentials (IPs) for n = 2-40 in photoionization experiments. A continuous decrease to 3.1 eV is found from n = 2 to 6 and a constant value of 3.07 ± 0.06 eV for n = 10-40. This IP evolution is similar to the sodium-water and the sodium-methanol system. Quantum chemical calculations (B3LYP and MP2) of the IPs indicate adiabatic contributions to the photoionization process for the cluster sizes n = 4 and 5, which is similar to the sodium-methanol case. The results of the extrapolated IPs and the vertical binding energies (VEBs) of cluster anions are compared with the recently reported VEBs of solvated electrons in liquid water, methanol, and ethanol solutions in the range of 3.1-3.4 eV. The new results imply that the extrapolated VBEs of solvated electrons in anionic clusters match the VBE in liquid water, while they are about 0.5 eV too low for methanol. The influence of the presence of counterions on these findings is discussed.

Temperature evolution in IR action spectroscopy experiments with sodium doped water clusters

“…The onset of melting triggers the IR signal and blocks the characteristic band and thus reduces further heating. In principle this mechanism can be applied to other sodium doped, hydrogen bonded clusters, 27,72 when solvated electrons are formed. However, this is not the case for nitrogen containing solvents [73][74][75] and probably other clusters, where the scavenging of the sodium 3s electron by molecules with high electron affinity occurs.…”

Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

“…It has been speculated that the phase of these methanol clusters may more closely resemble solids than liquids. 69 In light of the difference from the binding predicted binding energy, the correspondence between the extrapolated lifetime and the bulk measurement requires future consideration.…”

Photoionization and vibrational spectroscopy of sodium doped water clusters

“…[45,47,140] Compared to ionization methods such as EI and VUV photoionization, photoionization of sodium doped clusters was concluded to be mostly fragmentation free for photons energies below 5 eV. [46][47][48] Despite the inability of mixed cluster detection of N 2 O and NO 3 − containing particles [141,142] due to intra-cluster reactions, a variety of sodium doped clusters such as benzene, [35] water, [42] methanol, [42] ethanol, [42] 2-aminoethanol, [139] acetic acid, [140] dimethyl ether, [40] ammonia, [39] and rare gases [46] have been produced and detected.…”

“…[63,70] It was found that, when a sodium atom is added to a hydrogen bonded cluster, the ionization threshold energy decreases from 5.139 eV for atomic sodium [62] to cluster size and constituent dependent values. [42,63,70,106,139] A comparison of the appearance ionization energies for different cluster sizes shows that small clusters with n ≤ 4 show a decreasing aIE with increasing n, whereas clusters with n ≥ 4 have a constant aIE of 3.17 ± 0.05 eV, [38,63] , see black filled squares in Figure 2.3. This aIE has been assigned to clusters from the so-called isomer class I.…”

“…[29] In contrast to the phenol method, photoionization of alkali metal doped water clusters is considered to be free of fragmentation if performed close to the ionization threshold. [34,36,37] Sodium doping is a suitable technique for the detection of pure, nm-sized particles and clusters of several compounds, like water, [38] ammonia, [38][39][40] alcohols, [41][42][43] toluene, [44] propane, [44] dimethylether, [40] acetic acid, [45] and rare gases. [46] Therefore sodium doping has been applied as a reference technique to study the fragmentation of clusters caused by other ionization methods.…”