J. I. Steinfeld

Infrared Double Resonance in Sulfur Hexafluoride

The relaxation of sulfur hexafluoride has been monitored by observation of infrared absorption intensities following passage of an infrared laser pulse through the gas. The laser pulse saturates a small number of rotational lines in the ν3 ← 0 transition of SF6 at 944 cm−1, producing a transient “hole” in the absorption spectrum at that frequency. This hole is filled in very rapidly by rotational relaxation processes. The specific vibrational excitation is, at essentially the same time, transformed into a vibrational temperature in excess of the gass translational temperature, by means of very efficient vibration ↔ vibration energy transfer collisions. The energy released in this step also heats the gas translationally by the order of 25°K. The vibrational temperature then relaxes to the translational temperature by a binary collision process, with pτ = (122 ± 8) μsec·torr in pure SF6. The rate‐controlling step is concluded to be the vibration→translation relaxation of the ν6 level at 363 cm−1. The mean ...

Critical Survey of Data on the Spectroscopy and Kinetics of Ozone in the Mesosphere and Thermosphere

Spectroscopic data and reaction rate coefficients pertinent to ozone in the mesosphere and thermosphere (altitude >50 km) are critically surveyed. These data should be of use in modeling atmospheric infrared luminescence, measuring atmospheric ozone concentrations by remote sensing, and designing and interpreting laboratory measurements. There is a clear need for additional data on metastable ozone electronic states, additional atmospheric ozone formation channels, collision processes involving electrons and ions, and vibrational state dependence of reaction rate coefficients.

Analysis of perturbations in the A2Π-X2Σ+ “Red” system of CN

Abstract Deperturbed vibration-rotation constants of the A 2 Π( v ′ = 0 to 12) and X 2 Σ + ( v ″ = 0 to 8) states of CN are obtained. Specroscopic data from several sources are combined using a weighted, nonlinear least-squares fitting routine. The diagonalized effective Hamiltonian matrix contains as many as two 2 Π and four 2 Σ + mutually interacting vibronic levels. Perturbations of A 2 Π by both X 2 Σ + and B 2 Σ + are treated simultaneously. The deperturbed constants and interaction matrix elements obtained provide a significantly more accurate representation of all perturbed and unperturbed observed lines than the previously reported values. The electronic factors of the spin-orbit and rotation-electronic perturbation matrix elements for the A ∼ X and A ∼ B interactions are determined and several previously unreported perturbations are detected and analyzed. Merged constants and Dunham coefficients are calculated; a detailed statistical treatment of the parameters and error estimates has also been carried out.

Energy‐Transfer Processes in Monochromatically Excited Iodine Molecules. III Quenching and Multiquantum Transfer from υ′ = 43

The fluorescence arising from absorption of the 5145‐A laser line by molecular iodine vapor has been analyzed. Quenching and vibrational and rotational energy‐transfer efficiencies for collision between the excited iodine and other gases (ground‐state I2, He, Ne, Ar, Kr, Xe, H2, and CO2) have been determined, using a numerical solution of the master equation for relaxation. Vibrationally inelastic processes with Δυ′ ranging from + 5 to − 8 have been observed; their relative magnitudes appear to be well predicted from the oscillator matrix elements of the intermolecular potential coupling terms, properly weighted by a detailed balancing factor.

Collision-induced predissociation by van der Waals' interaction

Abstract We have developed a theory that satisfactorily predicts the relative magnitudes of the observed fluorescence quenching cross sections for B(3ΠO+u)I2, based on van der Waals perturbation. Applications to other systems are also discussed.

Deposition of refractory metal films by rare-gas halide laser photodissociation of metal carbonyls

Films of Cr, Mo, and W on quartz, Pyrex, Suprasil, and Al substrates were deposited by photodissociation of the respective hexacarbonyls using focused and pulsed radiation from rare‐gas halide lasers. Cr was deposited by dissociation of Cr(CO)6 using XeF (308 nm), KrF (249 nm), and ArF (193 nm) lasers. Mo and W were deposited from their respective hexacarbonyls at 249 and 193 nm. Pulse energies varied between 8 and 12 mJ. Pulse rates of 10–60 Hz were used. The pulse duration was about 10 ns. Depositions with substrates both parallel and perpendicular to the excimer radiation were attempted. Only in the case of perpendicular configuration were strongly adherent films observed. The deposition rates for thicknesses up to 3000 A appeared to be independent of the pulse rate for all three metals. The films exhibited strong adhesion to the substrate. Scanning electron microscope photographs of the films revealed the presence of continuous metal layers. Auger and x‐ray analyses of the films indicated contaminatio...

Near-infrared surface-enhanced Raman scattering of trinitrotoluene on colloidal gold and silver

Abstract We report surface-enhanced Raman scattering (SERS) from trinitrotoluene (TNT) adsorbed on colloidal silver and gold in aqueous solutions. Spectra were measured with a fiber optic probe using a diode laser at 830 nm as the excitation source and a charge-coupled device (CCD) as the detection system. Different types of surface-enhanced Raman spectra and enhancement factors have been observed on these metals, indicating differences in adsorption of TNT on gold and silver. Spectra were measured down to 10 −7 M TNT in colloidal gold solution, corresponding to a sensitivity of less than 1 pg TNT. Our results demonstrate the potential of SERS for probing TNT with high sensitivity and specificity, and suggest SERS on colloidal gold as a powerful method for detection of TNT and similar species at ultratrace levels.

Energy‐Transfer Processes in Monochromatically Excited Iodine Molecules. V. Rotational Energy Transfer in Argon‐Excited I2

Rotationally resolved energy‐transfer rates have been measured for I2 excited to J′=11 and 15 of v′ = 43 of the B 3Π0u+ state by the argon laser line at 5145 A, for accompanying changes in v′ of 0, ± 1, ± 2, and ± 3, in collisions with ground‐state I2, H2, He, and Ne. In all of these collisions, there is a persistence of rotational state, | Δ J′  | ≤ 14 being favored; however, broader distributions are found, as expected, for collisions with larger |Δ v|s or with heavier collision partners. The microscopic rate constants are asymmetric to Δ J′>0, as expected for (T/B)1/2 ≈ 80.

Infrared saturation in sulfur hexafluoride

The saturation of absorption of a CW infrared laser beam by SF6 has been measured as a function of pressure of SF6 and added buffer gases (He, Kr, and C2H6). The results are interpreted by means of a four-state linear kinetic model for saturation of vibrational energy levels by intense infrared radiation, which predicts equalization of upper and lower level populations at power densities of approximately 10 W/cm2. Vibrational and rotational deactivation cross sections are derived from these data with the aid of this model, which suggests that previously observed pulse transparency effects may be interpreted in terms of this same model.

Infrared absorption of explosive molecule vapors

Abstract Infrared absorption spectra have been obtained for the high explosive molecules TNT, RDX, and PETN in the vapor phase. Integrated band strengths were measured for the symmetric and antisymmetric -NO 2 vibrations in each of these molecules. Ab initio calculations of vibrational frequencies and intensities were carried out for comparison with the experimental data. Previous measurements of the heats of vaporization of these materials were checked using the temperature dependence of infrared band intensities. Measurements were also carried out on ammonium nitrate; in this case, only the decomposition products NH 3 , HNO 3 , and N 2 O were observed in the vapor phase in equilibrium with the solid.