Emission from several electronically excited states of NS is observed when the energetic molecule S4N4 is photolyzed with radiation from an excimer laser. Photolysis at 248 nm generates fluorescence from the B 2Π1/2,3/2, H 2Π1/2, G 2Σ−, and I 2Σ+ states of NS. NS(B 2Π1/2,3/2) and NS(C 2Σ+) fluorescence is observed when the photolysis wavelength is changed to 222 nm. The NS(H) and NS(C) spectra are postulated to arise from a resonant interaction between the KrF and KrCl excimer photons, respectively, and vibrationally hot ground state NS. LIF excitation scans on the NS X 2Π1/2,3/2 → B 2Π1/2,3/2 system confirm the production of rotationally and vibrationally excited NS(X) up to v″=4. A mechanism, based on the experimental data (i.e., spectral composition, laser fluence studies, excited state time histories), calculated heats of formation, and Gaussian molecular orbital calculations, is proposed to account for the observed emissions. For photolysis at 248 nm it is hypothesized that a two photon absorption promotes the ground singlet state of S4N4 to an upper repulsive singlet state, which rapidly dissociates (τ≪30 ns), producing an acyclic S3N3 fragment and vibrationally excited monomeric NS(X). The photofragments can interact further with the excimer radiation to produce NS(B) and NS(H), respectively. A similar mechanism is proposed to account for the presence of the NS(B) and NS(C) excited states for the 222 nm photolysis.
The Cartesian magnetically insulated transmission line (MITL) theory of Mendel et al. [Appl. Phys. 50, 3830 (1979); Phys. Fluids 26, 3628 (1983)] is extended to cylindrical coordinates. A set of equations that describe arbitrary electron flows in cylindrical coordinates is presented. These equations are used to derive a general theory for laminar magnetically insulated electron flows. The laminar theory allows one to specify the potentials, fields, and densities across a coaxial line undergoing explosive electron emission at the cathode. The theory is different from others available in cylindrical coordinates in that the canonical momentum and total energy for each electron may be nonzero across the electron sheath. A nonzero canonical momentum and total energy for the electrons in the sheath allows the model to produce one-dimensional flows that resemble flows from lines with impedance mismatches and perturbing structures. The laminar theory is used to derive two new self-consistent cylindrical flow solutions: (1) for a constant density profile and (2) for a quadratic density profile of the form ρ=ρc[(r2m−r2)/(r2m−r2c)]. This profile is of interest in that it is similar to profiles observed in a long MITL simulation [Appl. Phys. 50, 4996 (1979)]. The theoretical flows are compared to numerical results obtained with two-dimensional (2-D) electromagnetic particle-in-cell (PIC) codes.
The 248 nm photodissociation of KI: Determination of the branching ratio of K(42 P J ) doublets in the presence of Ar, H2, and N2 J. Chem. Phys. 99, 9603 (1993); 10.1063/1.465493Ultraviolet absorption cross sections for N2H4 vapor between 191-291 nm and H(2 S) quantum yield in 248 nm photodissociation at 296 K S4 N4 was photolyzed by the KrF excimer laser source at 248 nm. The excited state photofragments produced are the NS(B 211) rand NS(H 211) 1/2' NS( G 2~ -) and NS(l2~ + ) states. Single band progression fluorescence out of v' = 0 for NS (H) 1/2 and v' = 2 for NS (G,/) are observed. Franck-Condon factors have been calculated for NS(H). up to v' = 3. The electronic transition moment for the NS(H-X) transition was found to decrease slightly with increasing r. The radiative lifetime of the 0,5 band ofNS(H) 112 is determined to be 87 + 11 ns.The collisional quenching constants at 335 K for various species including N2 -(k q = 3.4 ± 0.7 X 10-10 cm 3 s -1), CF 4 (k q = 1.8 ± 0.4 X 10-10 cm 3 s -1), SF 6 (k q = 3.9 ± 0.7X 10-10 cm 3 s -1) and He (k q = 5.6 ± 2.2x 10-11 cm 3 s -1) are reported. A semiempirical calculation using a PM3 Hamiltonian was used to calculate the heats of formation of various (SN) x species. A mechanism is proposed to account for the presence of these excited states based on laser fluence, excited state time histories, spectral composition and calculated heats of formation. NS(B) is postulated to arise directly from an intermediate photolysis product which is assumed to be acyclic S3 N 3' The NS (H 211) 1/2 subband, NS( G 2~ -) and NS(l2~ + ) states are thought to be produced from a resonant interaction with the KrF line at 248 nm and vibrationally excited ground state NS. Using the 12 (D i g -A iu ) emission as an actinometer, the overall efficiency on the conversion of absorbed photons by S4N4 into NS(B 2n) is 2.6 ± 0.7%. M Sep) + N(4S) + M --+NS(a 411)~NS(b 4~ -) M --+NS(B 2IT),
A discharge flow apparatus was used to study the chemiluminescence of NS(B2II) resulting from the S(3P) + 3( 2 ) reaction. Ground-state sulfur atoms and azide radicals were produced by the reaction of excess fluorine atoms with H2S and HN3, respectively. The S + N3 reaction produces 8( 2 ) chemiluminescence in the region from 290 to 520 nm with an NS(B2n-* 2 ) photon yield of 0.06%. The 8( 2 ) branching fraction is viewed in terms of the many reactive surfaces present in this reaction. A spectral simulation code was written to obtain the vibrational populations and rotational temperatures of NS(B). The steady-state vibrational population revealed an inverted distribution with N""2 > N"m1. A bimodal rotational distribution is thought to occur with the initial rotational envelope approximated by an effective temperature of 1200 K.
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