Velocity of a Molecule Evaporated from a Water Nanodroplet: Maxwell–Boltzmann Statistics versus Non‐Ergodic Events

Abstract

The velocity of amolecule evaporated from amassselected protonated water nanodroplet is measured by velocity map imaging in combination with ar ecently developed mass spectrometry technique.T he measured velocity distributions allowp robing statistical energy redistribution in ultimately small water nanodroplets after ultrafast electronic excitation. As the droplet sizei ncreases,t he velocity distribution rapidly approaches the behavior expected for macroscopic droplets. However,adistinct high-velocity contribution provides evidence of molecular evaporation before complete energy redistribution, corresponding to non-ergodic events.The evaporation of water occurs through the breaking of one or several hydrogen bonds.T hese hydrogen bonds are responsible for many of the remarkable features of water [1] that are essential to life.W ater is known for its exceptional ability to absorb and hold heat at the macroscopic level, whereas at the sub-microscopic level, the intermolecular transfer of vibrational energy is known to be ultrafast because of the strong interactions between OÀHo scillators. [2,3] Thequantitative description of energy transfer in hydrogen-bonded compounds after electronic excitation is particularly challenging. Foralarge water droplet, the evaporation of water manifests itself as av elocity distribution of the evaporated molecules obeying Maxwell-Boltzmann (MB) statistics as ar esult of energy equipartitioning in athermalized system. In the present letter we address the thermalizing ability of even as mall water droplet following the sudden excitation of one of its molecules.Protonated water nanodroplets,H + (H 2 O) n=2-8 ,a re produced by supersonic expansion followed by electron impact ionization and acceleration at 8keV energy.T hey are then mass-and velocity-selected more than 1 msa fter being formed.[4] As ingle high-velocity collision (with V i in the laboratory frame ranging from 10 5 to 2.10 5 ms À1)w ith an Ar atom leads to energy deposition in the droplet by electronic excitation [5] of one of the molecules on atypical time scale of af raction of af emtosecond.[6] High-velocity collisions [7,8] probe ab road range of energy deposition, in contrast to Figure 1. Velocity map imaging of molecules evaporated from water nanodroplets. Evaporation is induced by asingle collision between amass-selectedprotonated water nanodropleta nd an argon atom. The nanodroplet has aselected laboratoryframe velocity V i before the collision. The evaporated H 2 Omolecule acquires an additionalt ransverse velocity, V t, (with respect to the original flight direction of the droplet) and reaches the detectorplaced at adistance D = 250 mm from the collision point. The impact position, R,o fthe evaporated molecule on the detector is related to the velocity, V,o fthe evaporated molecule in the center-of-mass reference frame of the nanodroplet.

Predicted structure and selectivity of 3d transition metal complexes with glutamicN,N-bis(carboxymethyl) acid

“…In case of the copper complex, one has a (well-known) strong Jahn-Teller effect which is responsible of the spatial structure far from a regular octahedron 75 S7), in good agreement with the experimental pKa4, equal to 9.4 27,79 As previously underlined, the small hydrogenated systems are poorly described by DFT, in particular within LDA or GGA approximations 80,81 . The reason is the self-interaction error energy which dramatically over stabilize the systems because of an over delocalization of the electronic density.…”

Predicting the activity of methoxyphenol derivatives antioxidants: II—Importance of the nature of the solvent on the mechanism, a DFT study

“…The solvation energy of proton H + and electron e À are roughly approximated by the used solvation model, since, because of the small size of these species, the electrostatic model is too crude, and one should use explicit water molecules to handle solvated electron and proton. For instance, the calculated energies of proton solvation have been found, at the similar level of calculation, equal to: À121.6 kcal/mol for H 2 O + H + à H 3 O + , and À129.8 kcal/mol for 2 H 2 O + H + à (H 5 O 2 ) + 28,29.…”