Stephen G. Kukolich

EPR spectra of C60 anion and cation radicals

Author Institution: Department of Chemistry, The University of Arizona; Department of Physics, The University of Arizona

Microwave spectra and structure of HI-HF complexes

Microwave spectra for the HI–HF, HI–DF, DI–HF, and DI–DF complexes were measured using a pulsed‐beam, Fourier‐transform microwave spectrometer. Rotational transitional transitions were measured over the 4–18 GHz range to an accuracy of 5 kHz. The spectroscopic constants obtained by fitting the observed transitions for the series HI–HF, HI–DF, DI–HF, and DI–DF are, respectively: (B+C)/2=2220.7482(8), 2173.236(2), 2209.623(4), and 2162.884(6) MHz; eQq(I)=687.01(2), 693.63(5), 725.96(4), and 727.8(1) MHz; ΔeQq(I)=−42(2), −50(6), −210(14), and −141(25) kHz; DJ =8.86(3), 8.25(6), 8.1(6), and 8.6(5) kHz. This complex has an interesting triangular structure with the H–I and H–F bonds making an acute angle of 70.1 (2.8)°. The iodine atom is coaxial with HF with a heavy atom separation R0(I–F)=3.660(8) A. Hyperfine structure due to deuterium quadrupole coupling and H–F spin–spin interactions was resolved and measured.

14NH3 Hyperfine Structure and Quadrupole Coupling

Hyperfine structure on the inversion transition for rotational states J–K = 2–1, 3–1, 4–2, 4–4, and 5–5 was measured with a high‐resolution beam maser spectrometer. Variations of nitrogen quadrupole coupling strength were observed for different rotational states. Derivatives of quadrupole coupling strength with respect to molecular coordinates are given. Additional spin–spin and spin–rotational terms are present for K = 1 states. These terms are compared for J–K = 1–1, 2–1, and 3–1 states. A more complete specification of the nitrogen and hydrogen spin–rotation tensors is obtained with the new data.

Measurement of the Molecular g Values in H2O and D2O and Hyperfine Structure in H2O

Individual components of the Zeeman transitions in the rotational spectrum of H2O and D2O were resolved in fields of 25–30 kG. This allowed determination of the g values with greater accuracy than previous measurements. The g values obtained for H2O were g(523) = 0.6959 ± 0.001 and g(616) = 0.6565 ± 0.001. The g values obtained for D2O were gaa = 0.3233 ± 0.001, gbb = 0.3580 ± 0.001, and gcc = 0.3226 ± 0.001. Analysis of the combined results indicates that the g values for H2O are positive and that the values are gaa = 0.6650 ± 0.002, gbb = 0.7145 ± 0.002, and gcc = 0.6465 ± 0.002. Hyperfine structure on the 616 − 523 transition in H2O was observed in a maser spectrometer, and the spin–rotation and spin–spin coupling constants were obtained. The measured value of the rotational transition frequency was 22 235 079.85 ± 0.05 kHz. The magnetic susceptibility anisotropies and molecular quadrupole moments were determined in H2O.

The structure and molecular properties of the acetylene–HCN complex as determined from the rotational spectra

The microwave spectra for four isotopic species of a complex formed between acetylene and HCN have been obtained using the pulsed, Fourier‐transform method with gas pulsed into an evacuated Fabry–Perot cavity. The spectra indicate the complex to be a T‐shaped near‐prolate asymmetric rotor (κ=−0.993) in its ground vibrational state in which HCN lies on the C2 symmetry axis with the hydrogen atom of HCN pointing to the middle of the triple bond of acetylene. The carbon atom of HCN is situated 3.656 A from the acetylene center of mass. Nuclear quadrupole coupling constants for N are obtained for all four isotopes and deuterium quadrupole coupling constants are obtained for two isotopes. Various contributions to the electric field gradients at quadrupolar nuclei are discussed.

Structure and quadrupole coupling measurements on the NO dimer

Abstract Rotational transition frequencies for 14 NO- 14 NO, 14 NO- 15 NO, and 15 NO- 15 NO were measured using a pulsed-nozzle Fourier transform microwave spectrometer. Rotational constants for the different isotopic combinations allowed an unambiguous structure determination. The molecule is in a cis planar structure with a bond between the nitrogen atoms and an NNO angle θ = 99.6(2)°. The NN bond length is 2.236(1) A and the NO bond length is 1.161(4) A. Hyperfine structure due to nitrogen quadrupole coupling and spin-rotation interactions was observed and analyzed. Rotation constants, quadrupole coupling tensor, and spin-rotation tensor elements are given.

The rotational spectrum and molecular structure of the furan–HCl complex

The microwave spectrum of the furan–HCl complex in the ground vibrational state has been measured and assigned using a Fourier‐transform microwave spectrometer employing a Fabry–Perot cavity and a pulsed supersonic nozzle as a molecular source. Furan–HCl is planar, with the axis of the HCl subunit oriented along the a axis of furan, bisecting the oxygen–carbon angle. A hydrogen bond is formed between the HCl proton and the lone electron pair of oxygen. The spectroscopic constants for furan–H 35Cl in MHz are A″=9421.3(39), B″=1004.2001(27), C″=904.5526(26), τ1=−0.9392(12), τ2=−0.0751(2), τbbbb =−0.004 01(19), τcccc=−0.002 17(17), χaa=−52.803(17), χbb=25.626(54), and χcc=27.177(54). Rotational transitions for the isotopic species furan–H 37Cl and furan–D 35Cl were also measured and assigned. The oxygen–chlorine distance is 3.26(1) A. The binding of the HCl to oxygen, rather than to the π bonds between the β carbon atoms, was confirmed by measurements on the 2‐D furan–H 35Cl complex.

High resolution measurements of 14N, D quadrupole coupling in CH3CN and CD3CN

A molecular beam maser spectrometer was used to measure hyperfine structure on the J=1→ 0 rotational transitions in CH3CN and CD3CN. Measured nitrogen quadrupole coupling strengths are 1eqaaQ(N)=−4224.4 ± 1.5 kHz for CH3CN and eqaaQ(N)=−4229.3 ± 1.5 kHz for CD3CN. The deuterium quadrupole coupling strength along the C–D bond direction is eqzzQ(D)=167.5 ± 4.0 kHz Nitrogen quadrupole coupling is discussed in relation to the electronic structure. Spin‐rotation interaction strengths are reported. A convenient method for calculating matrix elements for hyperfine interactions in an arbitrary coupling scheme is presented.

Electric dipole moments of (HC15N)2 and HC15NH35Cl

Abstract The electric dipole moments of two linear hydrogen-bound complexes containing HCN have been measured using pulsed Fourier-transform microwave spectroscopy carried out in a Fabry-Perot cavity. The dipole moment of (HC 15 N) 2 is 6.552(35) D and the dipole moment of HC 15 NH 35 Cl is 4.817(24) D. Both measurements refer to the vibrational ground state.

Measurements of relaxation cross sections for NH3 and OCS with a molecular beam maser spectrometer

Scattering cross sections for beams of NH3 and OCS are measured using a molecular beam maser spectrometer. The scattering gases used are NH3, OCS, CF3H, CH3F, N2, and He. In order to determine elastic and inelastic contributions to relaxation cross sections, measurements are made for (I) scattering of pure inversion or rotational state molecules, (II) scattering of molecules in a coherent superposition state, and (III) scattering of the whole beam in a distribution of rotational states. For dipolar scattering gases the cross sections for superposition states (σII) are significantly smaller than cross sections for pure states (σI). A theory of the scattering is presented in terms of phenomenological Redfield parameters and the S matrix. The theoretical description of scattering is used to separate elastic and inelastic contributions to the measured cross sections.