S. Coy

ABSTRACT Current progress on the rotational assignment of NH3 vibrational bands from 4800 cm−1 to 18 000 cm−1 is reported. We discuss a vibrational Hamiltonian for regions containing overtones or combinations of the three normal modes, excluding the symmetric inversion motion. The Hamiltonian is capable of modeling the normal mode to local mode transition observed in the spectrum as well as the observed band origins, rotational constants and intensifies. It includes the Darling—Dennison (local mode—normal mode) coupling, the (ν1 ν3)-2ν4 Fermi resonance, and one significant (ν1 ν3)-ν2 interaction. We illustrate the intramolecular vibrational dynamics predicted by the model Hamiltonian.

Many trace species of critical importance in atmospheric processes, notably ozone and methane, can be monitored by remote sensing of their infrared absorption and emission bands. Recovery of accurate column densities and mixing ratios from field measurements requires accurate knowledge of band parameters, viz., assigned line frequencies, line intensities, and pressure-broadened linewidths. The last-named quantities are generally derived from line-broadening models which have been tested against only a limited experimental data base. We have been using time-resolved infrared double-resonance spectroscopy to measure inelastic collision rates, which are a key component of broadening models. A pulsed infrared laser is used to prepare selected rovibrational levels of the species of interest; these are probed by a tunable semiconductor diode laser which provides the resolution necessary for resolution of energy-transfer processes at the state-to-state level. Results obtained for several systems indicate that in many cases the fast-order collision models used to account for rovibrational relaxation and collision broadening are inadequate to describe the inelastic processes in detail, particularly for large J and K changes in collisions.

... Bernd Abel,a) Stephen L. Coy, Jody J. Klaassen, and Jeffrey I. Steinfeld Department 0/ Chemistry and GR Harrison Spectroscopy Laboratory, Massachusetts Institute o ... Rates of collision-induced symmetry change (a++s) in V2 = 1 are on the order of kas = 4 f-lS - 1 torr - I, smaller ...

Assignments have been carried out for the 2ν3/(ν3+ν6)/2ν6 (triad)←ground state overtone bands and the triad←ν3/ν6 hot-band system of CHD3. A vibrational extrapolation method, using correspondences between a spherical-tensor formalism and the more conventional description of symmetric-rotor spectra, was used to facilitate the assignment and analysis of these bands. The resulting assignments have been confirmed by time-resolved double-resonance measurements.

High-resolution (0.013 cm-1) spectra of the second overtone of the OH stretch of trans-nitrous acid were recorded between 10 230 and 10 350 cm-1. The spectra were analyzed to yield a complete set of rotational parameters, including the A, B, and C rotational constants and the 5 quartic distortion constants. Two groups of anharmonic perturbations were observed and analyzed, and

An atmospheric-pressure air microplasma is ignited and sustained in a 25 µm wide discharge gap formed between two co-planar gold electrodes. These electrodes are the two ends of a microstrip transmission line that is microfabricated on an Al2O3 substrate in the shape of a split-ring resonator operating with a resonant frequency of 895 MHz. At resonance, the device creates a peak gap voltage of ∼390 V with an input power of 3 W, which is sufficient to initiate a plasma in atmospheric pressure air. Optical emission from the discharge is primarily in the ultraviolet region. In spite of an arc-like appearance, the discharge is not in thermal equilibrium as the N2 rotational temperature is 500–700 K. The intrinsic heating of the Al2O3 substrate (to 100˚C) causes a downward shift in the resonant frequency of the device due to thermal expansion. The temperature rise also results in a slight decrease in the quality factor (142> Q> 134) of the resonator. By decreasing the power supply ...