Velocity dependence of collisional alignment of oxygen molecules in gaseous expansions

Aquilanti, Vincenz̊o; Ascenzi, Daniela; Cappelletti, David; Pirani, Fernando

doi:10.1038/371399a0

Cited by 159 publications

(148 citation statements)

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“…The alignment degree, obtained by paramagnetism measurements [20] and confirmed by molecular scattering experiments [19], can be varied in a controlled way [19]. The two extreme cases are reported in the lower panel of Fig.…”

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“…Hot effusive beams contain fast rotating and randomly oriented molecules, while the "seeding" phenomenon associated with the supersonic expansion naturally leads to a rotational cooling and to a strong alignment of the rotational angular momentum. This phenomenon can be exploited to produce beams of projectile molecules slowly rotating with a controlled alignment degree [20]. Collisional experiments with "hot" effusive beams mainly probe the isotropic component of the interaction potential while those performed with aligned oxygen molecules uniquely probe the anisotropy of the surfaces [19].…”

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“…Total cross sections from supersonic seeded beams of O 2 (essentially in the ground rotational state, K 1 [20,22]) have been measured at various alignment degrees of the O 2 projectile molecule, given by the ratio W 0 ͞W 1 of the weights for the two possible K projections (0 or 1). The alignment degree, obtained by paramagnetism measurements [20] and confirmed by molecular scattering experiments [19], can be varied in a controlled way [19].…”

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Quantum Interference Scattering of Aligned Molecules: Bonding inO4and Role of Spin Coupling

et al. 1999

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Molecular beam experiments on collisions between oxygen molecules were performed at low energy and high angular resolution to permit observation of the "glory" interference effect. A novel technique for aligning the rotational angular momentum of the colliding molecules is exploited. Analysis of total scattering cross section data yields for the O 2 -O 2 bond an energy of 1.65 6 0.08 kJ ? mol 21 for the most stable configuration (parallel molecules) at a distance of 0.356 6 0.007 nm. These results indicate that most of the bonding in the dimer comes from electrostatic (van der Waals) forces but chemical (spin-spin) contributions are not negligible. [S0031-9007(98) The interactions of molecular oxygen are of vital importance in a number of fields such as combustion and, particularly, atmospheric physics and chemistry. Despite continuing efforts, some of the processes linked to the release and recombination of oxygen in its various forms are still far from being properly understood. Among these, those involving the oxygen dimer ͑O 2 ͒ 2 are particularly interesting both for the peculiar nature of the bond [1,2] and for their relation to the atmospheric ozone and atomic oxygen balance, through the highly endothermic reaction [10]. For the latter, three different phases, two of which are paramagnetic, are known but their modeling is not fully understood. Finally, spectra of the dimers show several weak absorption bands [11]. They are observed in the atmosphere and in oxygen under pressure or as a liquid and their assignment is far from complete. Some occur in the same wavelength range as the Chappuis bands of ozone, hence affecting measurements of stratospheric ozone [11]. The intermolecular potential in the oxygen dimer continues to pose a challenge to the theory of weak chemical bonds, beyond van der Waals forces. Indeed, because of the open shell nature of the oxygen molecules in their 3 S 2 g ground electronic state, the interaction in the dimer depends not only on the intermolecular distance and on the relative orientation between two molecules, but also on the coupling of their spins [12]. This originates a singlet ground potential energy surface and two excited ones, of triplet and quintet character.Ewing et al. [13] were the first to reveal clearly the presence of ͑O 2 ͒ 2 dimers in the gas phase, by spectroscopic studies at low temperature in the IR and visible range. From the analysis of the collision induced absorption spectrum they concluded that the dimer, a floppy molecule, is stabilized both in the ground and the excited electronic state [dissociating to O 2 ͑ 1 D͒ 1 O 2 ͑ 1 D͒] by a weak bond of van der Waals nature with well depths of 1.0 and 0.6 kJ ? mol 21 , respectively. They also give an equilibrium distance of ϳ0.35 nm tentatively associated with a parallel (H-like) geometry but provide no information on spin coupling and on the dependence of the interaction on the mutual orientation of the molecules.As for the magnetic properties of oxygen dimers in the gas phase an early study [14] of Stern-...

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Quantum Interference Scattering of Aligned Molecules: Bonding inO4and Role of Spin Coupling

et al. 1999

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“…Electrostatic hexapoles [1][2][3][4] have been introduced several year ago and employed in the alignment and rotational state selection of molecules of increasing complexity (for alignment in gaseous streams see reference [5], in particular oxygen 6 , benzene 7 and vortices 8 ). They were initially applied to linear and symmetric-top molecules, while more recently they have been successfully applied to molecules of higher complexity such as the chiral molecules propylene oxide 9,10 (for a characterization of the reaction pathways of propylene oxide see reference [11]) and 2-bromobutane 12 (see also reference [13]).…”

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Rotational state-selection and alignment of chiral molecules by electrostatic hexapoles

Palazzetti¹,

Lombardi²,

Nakamura³

et al. 2016

AIP Conference Proceedings

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Abstract. Electrostatic hexapoles are revealed as a powerful tool in the rotational state-selection and alignment of molecules to be utilized in beam experiments on collisional and photoinitiated processes. In the paper, we report results on the application of the hexapolar technique on the recently studied chiral molecules propylene oxide, 2-butanol and 2-bromobutane, to be investigated in selective photodissociation and enantiomeric discrimination.

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“…Stereodynamics in O 2 -surface interaction is, however, still far from being properly understood despite its great technological importance in heterogeneous catalysis, corrosion, and semiconductor industry. Previous studies employing aligned O 2 beams prepared with collisional alignment [1][2][3] or magnetic hexapolar field [4][5][6] have unveiled steric effects in O 2 chemisorption on Si(100), 4 Al(111), 5 clean 1 and adsorbed Pd(100) 2 surfaces. All of them, however, concern the polar angle effect of the O 2 axis; i.e., the difference in O 2 reactivity between the cases of side-on and end-on collisions.…”

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Communication: Fully alignment-specified O2 chemisorption on vicinal Si(100)

Kurahashi

Yamauchi

2014

The Journal of Chemical Physics

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A fully alignment-resolved O2 sticking experiment on a single domain Si(100)-(2×1) surface is presented. This provides the first experimental evidence that the reactivity of O2 depends on both the polar and azimuthal angles of the molecular axis relative to a surface. It has been found that, in case of side-on collision, an O2 molecule perpendicular to the dimer on Si(100) is about 40% more reactive than that parallel to the dimer. Comparison of the O2 sticking on flat and vicinal Si(100) surfaces indicates that barrierless dissociation channels exist at the double layer step.

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Velocity dependence of collisional alignment of oxygen molecules in gaseous expansions

Cited by 159 publications

References 30 publications

Quantum Interference Scattering of Aligned Molecules: Bonding inO4and Role of Spin Coupling

Quantum Interference Scattering of Aligned Molecules: Bonding inO4and Role of Spin Coupling

Rotational state-selection and alignment of chiral molecules by electrostatic hexapoles

Communication: Fully alignment-specified O2 chemisorption on vicinal Si(100)

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