Electrostatic Hexapole Field Research Articles

Virtual angular momentum: The dynamics of inverting molecules in an electrostatic hexapole field

The semiclassical dynamics of a molecule which undergoes tunneling inversion while traversing an electrostatic hexapole field is shown to be described by the motion of a two dimensional harmonic oscillator with angular momentum Lv. Analytical expressions are provided which show explicitly the dependence of Lv on the molecular inversion frequency. A comparison between calculated and experimental focusing curves is also presented.

A Voltage-Modified Trajectory Simulation for a State-Selected CH3I Supersonic Beam in an Electrostatic Hexapole Field

Abstract The |JKM > state selection of a seeded CH3I/Ar supersonic beam has been achieved using a 2-m electrostatic hexapole field. Several |JKM > states were better resolved than the previous one in a CH3Cl/He supersonic beam. A voltage-modified trajectory simulation was carried out for fitting the observed focusing curve, in which the first-order approximation of the Stark effect was corrected in terms of the hexapole voltage in an empirical formula. A better agreement was found on the peak positions of the focusing curve, and the relative heights of the three peaks suggest that CH3I molecules in the present beam populate among the |JKM > states in a statistical way with a rotational temperature of 3 K.

Formation of the State‐Selected CH Radical Beam and its Application to The CH + NO Reaction

The CH(X2II) radical beam was produced via the decomposition of methanol by a dc‐discharge in a pulsed supersonic beam. The CH radical beam was rotationally state‐selected and separated from other discharge products by using an electrostatic hexapole field. The chemiluminescence from the reaction of CH in the |3/2, 3/2, 3/2> state with NO was measured under the crossed beam condition. The wavelength region of the present chemiluminescence confirms no NH(A3II) formation. The formation of HCN(X) and/or OH(X2II) is tentatively proposed.

Formation of an intense pulsed beam of CH3Cl in the ‖111≳ state using a 2-m electrostatic hexapole field

An intense pulsed beam of CH3Cl in the ‖111≳ state without velocity selection was focused using a 2-m electrostatic hexapole field. The beam intensity was estimated to be ∼1×1013 molecules pulse−1, which is much greater than the similar beams in the earlier study of Gandhi et al. by at least two orders of magnitude. The beam had a 3-ms pulse width and was focused with an angular divergence of 0.7 mrad. The improvements in beam intensity and in the divergence of the beam can be mainly ascribable to the efficient pumping of the hexapole field through the cylindrical electrodes, which enables us to employ the helium seeding to have the fast stream velocity, the narrow distribution of velocity, and the aerodynamic effects. Those factors altogether made the velocity selection of the beam unnecessary.

Focusing and state selection of NH3 and OCS by the electrostatic hexapole via first- and second-order Stark effects

Neither the linear molecule OCS nor the rapidly inverting pyramidal NH3 have conventional first-order Stark effects (SE) and so are not ideally focusable by an electrostatic hexapole field. However, strong focusing and state selection of these molecules by such a hexapole field has been achieved using the UCLA apparatus, consisting of a pulsed supersonic beam source, 3 m hexapole rods, and a mass spectrometer detector. For NH3, a single intense peak in the focused intensity curve I(V0) is obtained (where V0 is the ‘‘rod voltage’’). From the observed linear velocity dependence of V0, characteristic of focusing via second-order SE, the peak is assigned as the ‖JKMJ〉=‖11±1〉 state (the upper state of the JK=11 inversion doublet with para nuclear symmetry), previously quadrupole focused by Kay and Raymond (1986). In contrast, ND3 focuses like a symmetric top, as expected, with a quadratic velocity dependence characteristic of first-order SE. For OCS, the first three peaks in the I(V0) curve, showing quadratic velocity dependence, are assigned to the ‖JlMJ〉 states ‖111〉, ‖212〉, and ‖313〉, focused via first-order SE for the l-doubled excited bending vibrational state, analogous to that found by Stolte et al. (1986) for N2O. An intense peak at higher V0 is due primarily to the ‖JMJ〉=‖10〉 state of the ground vibrational state, i.e., the linear OCS focused by second-order SE, following the theory of English (1971).

Oriented molecule beams: pulsed, focused beams of methyl halides in pure JKM rotational states

Intense pulsed, seeded, velocity-selected (Δ v/ v ≈ 1%) beams of state-selected, oriented methyl halide molecules are produced and characterized in a focusing machine employing a 3 m electrostatic hexapole field with electron impact and laser ionization mass spectrometric detection. Essentially pure rotational state selection has been achieved for five JKM states, with ¦111 > the most intense beam at T r = 1.9 K.

Improved Space Focusing of Polar Diatomic Molecules in a System of Quadrupole and Hexapole Fields

This paper describes a method for the compensation of the spherical aberration of a polar diatomic molecule in an electrostatic quadrupole field. This perturbation, caused by the higher order terms in the Stark effect, limits the opening angle of the lens and is compensated by an electrostatic hexapole field placed in the middle of the quadrupole field where the influence is the strongest. A detailed mathematical treatment of the motion of a molecule in a composite lens is given and the calculations show that the transmission of the lens increases by a factor 5. Preliminary experiments confirm the theoretical predictions.

Space Focusing of Polar Diatomic Molecules Using Electrostatic Hexapole Fields

Space focusing of polar diatomic molecules using an electrostatic hexapole field is discussed, and it is shown that focused molecular trajectories in this type of field are properly described by a Jacobian elliptic function. Although a detailed mathematical treatment is given, emphasis is placed upon the physical nature of the trajectories. These results are applied to the design of a molecular beam resonance apparatus using hexapole fields, and it is shown that, in practice, several simplifying approximations (with little loss in accuracy) may be made which allow design calculations to be carried out using only a slide rule.