Direct Determination of the Permanent Dipole Moments and Structures of Al−CH₃CN and Al−NH₃ by Using a 2-m Electrostatic Hexapole Field

Abstract

The supersonic beams of the (1-1) metal-ligand complexes of Al-CH(3)CN and Al-NH(3) were produced by a laser evaporation method. Nondestructive structure selection of the complexes and the dipole moment determination were performed by using a 2-m electrostatic hexapole field. The experimentally determined permanent dipole moments are 1.2 +/- 0.1 D for Al-CH(3)CN and 2.7 +/- 0.2 D for Al-NH(3). We find that the dipole moment of Al-NH(3) becomes larger than that of neat NH(3), while the formation of the Al-CH(3)CN complex produces a smaller dipole moment than that of neat CH(3)CN on the other hand. We performed the ab initio calculations to draw out plausible complex structures and to clarify the bonding character after formation of the complex, and we made comparisons with the computational results done by several groups. The Mulliken population analysis suggests the Al-->CH(3)CN charge flow, but on the other hand the Natural population analysis indicates very little charge flow. For the Al-NH(3) complex, the polarization effect of NH(3) and the N-->Al sigma donation would enhance the dipole moment strength. However, there still remains a controversial disagreement between the theoretical predictions and the experimental results. Further experimental determination using the hexapole method for various metal-ligand complexes and clusters could reveal the basic nature of interaction in the complex systems in general, and this method would complement theoretical calculations.

Hexapole-Oriented Asymmetric-Top Molecules and Their Stereodirectional Photodissociation Dynamics

“…This is the technique of choice in this paper. Hexapoles were initially employed for the rotational state-selection of linear , and symmetric-top molecules, − and more recently on asymmetric tops , and in the selection of conformers of the asymmetric-top 2-butanol (for studies on dimers, see refs and ; for other applications of the hexapolar filters, see, e.g., ref ). Orientation is achieved by applying homogeneous electric fields to hexapole-aligned molecules, as implemented here.…”

“…This is the technique of choice in this paper. Hexapoles were initially employed for the rotational state-selection of linear 14,15 and symmetric-top molecules [16][17][18] , and more recently on asymmetric-tops 19,20 and in the selection of conformers of the asymmetric-top 2-butanol 21 (for studies on dimers see 22,23 , for other applications of the hexapolar filters see for example 24 ). Orientation is achieved by applying homogenous electric fields to hexapole-aligned molecules 25 , as implemented here.Other techniques to obtain molecular orientation make use of strong homogenous electric fields (bruteforce techniques) [26][27][28] , laser absorption techniques [29][30] and non-resonant intense laser techniques [31][32] .…”

Reaction Dynamics with Molecular Beams and Oriented Molecular Beams: A Tool for Looking Closer to Chemical Reactions and Photodissociations

“…The hexapole state selector could be such a one as we will see below. 52,53 Table 2 shows the experimental and calculated electric dipole moments of two kinds of metal-organoic molecule (1:1) clusters produced by a laser evaporation method. In the table, De/eV is the dissociation energy of cluster, m calc is the calculated dipole moment, m exp is the experimental value obtained by the electrostatic hexapole method.…”

“…The molecular orbital calculation indicates that this opposite behavior that can be ascribed to the polarization effect of CH 3 CN. 52 Fig. 6 shows another example of the non-destructive separation by uisng the hexapole field.…”

Control of conformers combining cooling by supersonic expansion of seeded molecular beams with hexapole selection and alignment: experiment and theory on 2-butanol

“…Thanks to their focusing properties, they have been widely employed in scattering experiments, where high beam intensity and high duty cycles are required, 19 and for the selective preparation, measurement of electric dipole moments and investigation of the structures of complexes and clusters (see for example ref. [20][21][22][23][24][25][26][27]. Only recently, beams of asymmetric-top molecules have been aligned and the rotational state distributions obtained.…”