Karen E. Kerr

Selection rules for nuclear spin modifications in ion-neutral reactions involving H3+

We present experimental evidence for nuclear spin selection rules in chemical reactions that have been theoretically anticipated by Quack [M. Quack, Mol. Phys. 34, 477 (1997)]. The abundance ratio of ortho-H3+ (I=3/2) and para-H3+ (I=1/2), R=[o-H3+]/[p-H3+], has been measured from relative intensities of their infrared spectral lines in hydrogen plasmas using para-H2 and normal-H2 (75% o-H2 and 25% p-H2). The observed clear differences in the value of R between the p-H2 and n-H2 plasmas demonstrate the spin memory of protons even after ion-neutral reactions, and thus the existence of selection rules for spin modifications. Both positive column discharges and hollow cathode discharges have been used to demonstrate the effect. Experiments using pulsed plasmas have been conducted in the hollow cathode to minimize the uncertainty due to long-term conversion between p-H2 and o-H2 and to study the time dependence of the o-H3+ to p-H3+ ratio. The observed R(t) has been analyzed using simultaneous rate equations ...

High-resolution infrared spectroscopy of isotopic impurity Q1(0) transitions in solid parahydrogen

We have made a high‐resolution infrared spectroscopic study of the Q1(0) (v=1←0, J=0←0) vibrational transitions of the isotopic impurities D2 and HD in solid parahydrogen. Each impurity has a spectrum composed of ∼100 sharp lines spread over ∼0.4 cm−1. The linewidths vary, but are on the order of 10 MHz. These spectra make clear: (1) the infrared Q1(0) transitions of J=0 isotopic impurities are induced by the quadrupolar fields of nearby impurity J=1 molecules; and (2) the spectral pattern of strong Q1(0) lines is due to the splitting of the M‐orientational levels of J=1/J=0 o‐D2 or J=1/J=0 HD nearest‐neighbor (nn) impurity pairs. With the aid of several theoretical works, the strong lines in the D2 and HD spectra can be individually and unambiguously assigned as specific quantum state Q1(0) transitions of nn impurity pairs containing p‐D2/o‐D2 or o‐H2/o‐D2, and o‐H2/HD, respectively. The assigned transitions of nn impurity pairs containing o‐H2 are confirmed by combination differences which agree to with...

High-resolution laser spectroscopy of the Qv(0) transitions in solid parahydrogen

Our recent high-resolution laser spectroscopy of theQv(0) (υ=υ←0,J=0←0) transitions in solid parahydrogen is discussed. The systems studied include the fundamental vibrational bands of impurity D2 and HD, the first and second overtones of parahydrogen, and the charge-induced spectrum ofγ-ray irradiated parahydrogen. Additionally, Stark and stimulated Raman-gain spectroscopies are applied to the solid. The linewidths are as sharp as 2 MHz HWHM, which is highly unusual for a solid. Our spectra demonstrate a variety of physical phenomena, particularly theΔk = 0 selection rule, as well asJ = 1/J = 0 pair intermolecular interactions.

Charge induced H2 spectrum in γ‐ray irradiated para‐H2 crystals

A sharp spectral line has been observed in γ‐ray irradiated para‐H2 crystals and assigned to the pure vibrational Q1(0)(v=1←0, J=0←0) transition induced via the Condon effect by charges distributed in the crystal. The remarkable sharpness and stability of the signal is reported and discussed.