Giles Henderson

MICROWAVE MEASUREMENTS OF THE ROTATIONAL SPECTRUM OF BUTADIENE IRON TRICARBONYL

The rotational spectrum of butadiene iron tricarbonyl was measured using a Flygare–Balle type microwave spectrometer. A total of 71 a‐dipole and c‐dipole transitions in the 5–17 GHz range were obtained for this asymmetric top transition metal complex. The ‘‘best fit’’ rotational constants are A=1005.4201(3) MHz, B=958.0408(2) MHz, and C=933.6865(3) MHz. Centrifugal distortion constants were also obtained in the least‐squares fit to the measured transitions. The present measurements indicate an upper limit of 40 kHz for splittings due to internal rotation, which places a lower limit on the barrier height of V3 ≥ 1.2 THz. The measured rotational constants are used to determine CO bond angles and the distances between Fe and the butadiene C atoms.

A rigid rod normal coordinate analysis, and van der Waals force field of acetylene–HCl

A normal coordinate analysis appropriate for two weakly bound rigid rods is developed. Asymmetric top centrifugal distortion constants and published vibrational frequencies are employed in the normal coordinate analysis to obtain the intermolecular force field and refinements in the structural parameters. The analysis permits a more accurate interpretation of the observed Cl quadrupole coupling constant suggesting that the hydrogen bonding in this complex causes a decrease in the magnitude of the electric field gradient at Cl by 8±1% from that in the free HCl monomer. These methods also suggest that hydrogen bonding decreases the electric field gradient at deuterium in C2H2⋅ ⋅ ⋅DF by 10% and increases the corresponding H–F bond length by 1%.

Microwave measurements and ab initio dynamics of the large amplitude ring puckering motion in 2-sulpholene

Microwave measurements were made on the rotational spectrum of 2‐sulpholene using a modified Flygare–Balle pulsed beam Fourier transform spectrometer. Analysis and calculations provided information on the large amplitude ring puckering vibration of this system. Twelve and six rotational transitions were measured for the v=0 and v=1 states of the ring puckering vibration, respectively. The transitions for each vibrational state were fitted to a Watson’s A reduced Hamiltonian including terms for quartic distortion yielding for v=0 the values B=2125.96(6), C=1983.28(8), ΔJK=0.664(4), ΔK=−0.34(4) MHz, and for v=1 the values A=3995(26), B=2128.3(1), C=1984.6(1), ΔJK=−0.8(1), ΔK=−32(6) MHz. Subsequently, ab initio calculations were performed at the self‐consistent‐field (SCF)/3‐21G*, MP2/6‐31G*, and MP4/6‐31G* levels of theory to determine the barrier to inversion. The MP4/6‐31G* barrier was ΔE=116 cm−1, and can be considered to be the most accurate barrier value calculated in this study. An ab initio potential...

Animated Vibrational Models of Triatomic Molecules

Embedded movies display multiple panels that allow each vibrational mode to be observed simultaneously along with the composite superposition of the individual modes.