Molecular Beam Electric Field Deflection: Theoretical Description

Heiles, Sven

doi:10.1007/978-94-007-7866-5_3

Cited by 2 publications

(3 citation statements)

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“…Hence in the presence of thermal as well as zero-point motion it is not obvious to what degree ionic dissociation in a realistic cluster environment translates into an unambiguous change in the distribution of charge within the cluster. There exists a convenient observable which directly reflects electrical charge distribution within a system: the electric dipole moment p. Indeed, measurements of |p| by electrostatic deflection of cluster beams have served as a valuable probe of structure and bonding [36][37][38]. However, there have been only few applications of the method to water clusters [39][40][41].…”

Section: Introductionmentioning

confidence: 99%

“…To identify mass peaks deriving from doped species, it is therefore necessary to deuterate one of the partners. We used a supersonic oven filled with H 2 O vapor and injected DCl gas from a capillary into the expansion zone.In a system whose dipole moment undergoes fluctuations and is statistically oriented along the electric field (often referred to as a "floppy" cluster), the probability of sampling a particular dipole configuration approximates a canonical distribution, and the effective linear susceptibility is then given by the Langevin-Debye formula with the temperature corresponding to the cluster's internal rovibrational temperature [36][37][38]:the time-averaged value of the cluster dipole moment along the deflection field direction. It is important to emphasize (see, e.g., the incisive discussion in the classic book of Van Vleck [55]) that the numerator represents the statistical mean square of the vector dipole moment of the system (in the absence of an external field).…”

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confidence: 99%

“…In a system whose dipole moment undergoes fluctuations and is statistically oriented along the electric field (often referred to as a "floppy" cluster), the probability of sampling a particular dipole configuration approximates a canonical distribution, and the effective linear susceptibility is then given by the Langevin-Debye formula with the temperature corresponding to the cluster's internal rovibrational temperature [36][37][38]:…”

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confidence: 99%

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Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

2015

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The electric dipole moments of (H 2 O) n DCl (n=3-9) clusters have been measured by the beam deflection method. Reflecting the (dynamical) charge distribution within the system, the dipole moment contributes information about the microscopic structure of nanoscale solvation.The addition of a DCl molecule to a water cluster results in a strongly enhanced susceptibility.There is evidence for a noticeable rise in the dipole moment occurring at n≈5-6. This size is consistent with predictions for the onset of ionic dissociation. Additionally, a molecular dynamics model suggests that even with a nominally bound impurity an enhanced dipole moment can arise due to the thermal and zero point motion of the proton and the water molecules. The experimental measurements and the calculations draw attention to the importance of fluctuations in defining the polarity of water-based nanoclusters, and generally to the essential role played by motional effects in determining the response of fluxional nanoscale systems under realistic conditions. 2 INTRODUCTION.Water clusters are convenient experimental platforms for the study of the microscopic physics and chemistry of solvation. By monitoring cluster properties as a function of the number of water molecules, it is possible to follow the step-by-step progression of intermolecular interactions [1], following the transition from isolated molecule to bulk By virtue of having a large fraction of their molecules located near the surface, clusters can serve as surrogates for important processes occurring on aerosols and hydrometeors [2,3]. Composed of only a finite number of constituents, they often serve as test beds for theoretical methods and models.Small water clusters doped with an acid molecule -here, for concreteness, hydrogen chloride -have been the subject of a great number of theoretical papers and a sizeable (but regrettably much smaller) number of experimental ones. Hydrogen chloride readily dissociates into H 3 O + and Cl -and the dissociation also takes place in HCl hydrates [4][5][6][7][8], on the ice surface [9][10][11][12] or on larger water nanoparticles [13][14][15] and protonated water cluster ions [16,17]. One inquiry that persistently threads its way through this subject is: what is the minimum quantity of water molecules, (H 2 O) n , required to dissociate the acid [18]? According to calculations, the acidically dissociated structure is supported starting from n=4; most of the theoretical approaches agree that at this size the dissociated form represents the global minimum on the potential energy surface [18][19][20][21][22][23][24]. Experimentally, for neutral clusters the question has been probed by laser spectroscopy (see, e.g., [25][26][27][28]) but finding a conclusive spectroscopic signature of the onset of dissociation in a nanocluster is not straightforward.As a matter of fact, the challenge is not just experimental but conceptual. The free water clusters in natural and laboratory environments generally exist at temperatures appreciably above absolute zero ...

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Section: Introductionmentioning

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Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

2015

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Structural, electronic and magnetic properties of stoichiometric cobalt oxide clusters (CoO)nq (n=3−10,q=0,+1): A modified basin-hopping Monte Carlo algorithm with spin-polarized DFT

Daud

2019

J. Theor. Comput. Chem.

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The structural, electronic and magnetic properties of the neutral and cationic cobalt oxide clusters (CoO)[Formula: see text] ([Formula: see text], [Formula: see text]) have been studied using a modified basin-hopping Monte Carlo (BHMC) algorithm refined by spin-polarized DFT. A systematic search of global minimum structures predicts new global minima of (CoO)[Formula: see text] and reproduced other minima that are in excellent agreement with previous works. For most low-spin and high-spin states, the structural transition from planar-like to compact structure occurs at (CoO)[Formula: see text], which is in contrast with the general notion that the structural changes at (CoO)[Formula: see text]. Supported by the results of the binding energy, second-order total energy difference, chemical hardness, chemical potential and HOMO-LUMO gap confirms the stability of (CoO)4. Results of the spin magnetic moments for the global minima show that (CoO)4 and (CoO)8 spin configurations exhibit a fully antiferromagnetic (AFM) ordering, while (CoO)9 spin displays the highest ferromagnetic (FM) ordering. Interestingly, elongation of Co–Co bond in (CoO)4 causes O being polarized by the neighboring Co atoms that accordingly follows the Goodenough-Kanamori-Anderson rule of FM super-exchange coupling for the Co-O-Co structural rearrangement to 90∘ ([Formula: see text] structure) in order to accommodate the spin magnetic ordering changes. This rearrangement is a result of the valence band being shifted away from the Fermi level to lower energy causing high population of the spin-up density of state and leading to the asymmetrical polarization of the whole (CoO)4 structure. As far as the dissociation energy surfaces are concerned, the first ever such surfaces are constructed corresponding to [Formula: see text], which identify a complete dissociation pathway linking the cationic and neutral clusters and finally confirm (CoO)[Formula: see text] as the most stable cluster compared to the rest.

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Molecular Beam Electric Field Deflection: Theoretical Description

Cited by 2 publications

References 98 publications

Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

Structural, electronic and magnetic properties of stoichiometric cobalt oxide clusters (CoO)nq (n=3−10,q=0,+1): A modified basin-hopping Monte Carlo algorithm with spin-polarized DFT

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