Laser-induced Resonance Fluorescence Research Articles

Channel and Analyte Dynamics in the High-Voltage Spark Discharge Using Raman, Fluorescence, and Emission Spectroscopies

An investigation was made of the use of laser light scattering and laser-induced resonance fluorescence, employed in combination with spontaneous emission, as diagnostic probes of the atmospheric-pressure high-voltage spark discharge, to elucidate information on various species. Raman scattering allowed the space- and time-resolved investigation of N2 behavior in the spark channel. Emission profiles of Al(I) and AlO were obtained to establish the temporal regions that were nonemitting for each species. Resonance fluorescence permitted observation of aluminum species in the nonemitting post-discharge torus both spatially and temporally resolved. The channel dynamics studies revealed the interaction of atmospheric nitrogen with the spark channel. Fluorescence studies on aluminum as the analyte species revealed the presence of Al(I) and AlO in the post-discharge torus region, after the discharge current has ceased, and after the Al(I) and AlO emission has ceased. This establishes that analyte material exists in more than one chemical form in the nonemitting regions of the spark discharge, and that excitation decays before all free atoms recombine into small molecules.

Rotational distribution of nascent OH radicals after H2O2 photolysis at 193 nm

The rotational distribution of OH(X2Π,v″=0) radicals was investigated by resonant laser-induced fluorescence (LIF) after photolysis of H2O2 at 193 nm. A microcomputer equipped LIF arrangement allowed special shot-by-shot normalization of the fluorescence signal for noise reduction. Using a least-squares procedure we were able to account for all measured line intensities including overlapping lines (blends) and obtain a complete rotational state distribution of the OH(X2Π,v″=0) state. The rotational excitation shows a Gaussian-like distribution with a maximum atK″=12 and with 16% of the total available energy (17,400 cm−1) appearing in rotation. Only 1% of the available energy is converted into vibration, leaving over 83% for translational excitation. The measured rotational distribution appears to fit a semiclassical theory.

Charge radii and moments of tin nuclei by laser spectroscopy.

The isotope shift and hyperfine structure of the optical Sn I resonance transition 5${p}^{2}$ $^{3}\mathrm{P}_{0}$\ensuremath{\rightarrow}5p6s $^{3}\mathrm{P}_{1}$ at \ensuremath{\lambda}=286.3 nm have been studied for 18 Sn nuclei including two isomers. Laser-induced resonance fluorescence from a collimated atomic beam of tin was observed using a tunable continuous wave dye laser with frequency doubler. The electromagnetic nuclear moments and changes of the mean square charge radii of the nuclear charge distributions were determined. The results are discussed with respect to the information they provide on the nuclear structure of the nuclei investigated; they are compared with various theoretical models.

Laser induced fluorescence as a technique for investigations of sputtering phenomena

Sputtering investigations by means of laser induced resonance fluorescence (LIF) using dye lasers are reviewed. The basic principles as well as various effects and experimental problems inherent to the method are briefly discussed. Some results on population distributions, velocity distributions of sputtered atoms in the ground state and metastable states, the influence of oxygen coverage as well as transient effects are presented. The discussion is intended to show the potential of the this method in sputtering investigations.

Laser spectroscopy of Li 3 isolated in Xe matrices, comparison with other metal triatomics

The laser-induced resonance fluorescence (Raman) of three lithium-containing species isolated in solid Xe is presented. In Xe, one finds in addition to a progression assignable to Li 2 two others both of which are assigned to Li 3, one, a fluxional molecule is characterized by a number of progressions in the symmetric stretch of the molecule (310 cm −1) built upon several vibronic terms, the other is ascribed to a rigid acute angle form of Li 3 characterized by a symmetric frequency of 353 cm −1 and a bending frequency of 231 cm −1. With yellow (R6G dye laser) excitation yet another species is excited which is tentatively assigned to Li 4.

The self-annihilation rate of metastable Mg atoms

The second-order rate coefficient for the self-quenching of Mg *(3s3p 3P J ) has been measured using. The time-resolved, laser-induced resonance fluorescence technique- The total bimolecular self-annihilation rate constant was determined to lie in the range of (0.7–6) × 10 −11 cm 3/s over the temperature range of 820–920 K.

Measurement of the nuclear quadrupole moment of53Cr by laser-Rf double resonance

The hyperfine structure of the metastable atomic states (3d 44s 2)5 D 1,2,3,4 of53Cr has been measured using theABMR-LIRF method (atomic beam magnetic resonance detected by laser induced resonance fluorescence). The dipole coupling constantsA and the quadrupole coupling constantsB are found to beA(5 D 1)=−17.624(2) MHzB(5 D 1)=−21.847(5) MHzA(5 D 2)=−25.113(2) MHzB(5 D 2)=−13.485(5) MHzA(5 D 3)=−35.683(2) MHzB(5 D 3)=15.565(5) MHzA(5 D 4)=−48.755(2) MHzB(5 D 4)=63.021(5) MHz. From these measured hfs constants the electric quadrupole moment for53Cr is calculated to beQ=−0.15 (5) barn. The 30% error takes into account the uncertainties due to configuration interaction effects (shielding and antishielding effects) and of deviations from pure SL-coupling for the states5 D 1,2,3,4.

Laser-rf double-resonance hyperfine structure measurements of the metastable 3d 4s 1 D 2 state of43Ca

The hyperfine structure of the (3(d 4s)1 D 2metastable state of43Ca has been measured using theABMR-LIRF method (atomic beam magnetic resonance, detected by laser induced resonance fluorescence). The measurements yielded for the magnetic dipole and electric quadrupole constantsA=−17.650(2) MHz andB=−4.642(12) MHz, respectively. From the measuredB factor the spectroscopic electric quadrupole moment (uncorrected for shielding effects) has been calculated to beQ(43Ca)=−0.062(12) barn. In addition, isotope shifts in the lines (3d 4s)1 D 2(3d 4p)1 F 3 0 and (3d 4s)1 D 2(4s 5p)1 p 1 0 for the stable calcium isotopes have been obtained by high resolution laser spectroscopy.

High precision measurements of the hyperfine structure of seven metastable atomic states of57Fe by laser-Rf double-resonance

The hyperfine structure of the metastable atomic states (3d74s)5F2,3,4,5 and (3d 7 4s)3F2,3,4 of57Fe has been measured using theABMR- LIRF method (atomic beam magnetic resonance detected by laser induced resonance fluorescence). From these measurements the following hfs constantsA of the magnetic dipole interaction have been obtained (corrected for second order effects):A(5F2)=55.994(7) MHzA(5F3)=69.632(5) MHzA(5F4)=78.435(4) MHzA(5F5)=87.246(3) MHzA(3F2)=143.328(4) MHzA(3F3)=50.602(10) MHzA(3F4)=13.456(5) MHz

On the nuclear spin and magnetic dipole moment of 180Ta

The hyperfine structure of an atomic transition in 180Ta was investigated by laser-induced resonance fluorescence. As a result we obtained for the quantity μ I 180 (1+ 1 2 I 180) the value 5.04 (5) μ N . This experimental result is best reproduced assuming parallel coupling of a 9 2 −[514] proton and a 9 2 +[624] neutron. It is concluded that 180Ta most likely has I π =9 − and a magnetic dipole moment μ I=4.77 (5) μ N.

Laserspectroscopic studies of collective properties of neutron deficient Ba Nuclei

Isotope shifts and hyperfine structure of the BaI resonance-line (λ=553.6 nm) have been measured by dye laser induced resonance fluorescence on an atomic beam for135m, 129g, 129m, 126Ba thus extending previous high resolution measurements of neutron deficient Ba nuclides (N<82). The experimental results, now available for 16Ba isotopes and isomers withA=140−126, are used to deduce differences of rms charge radii, magnetic dipole and electric quadrupole moments. While the groundstates display a pronounced odd-even staggering the h 11/2− isomers135mBa and133mBa show a decreased staggering. Conspicuously the isomer shift of theg 7/2+ isomer129mBa proves to be negative. The nuclear structure information is discussed in the context of gammaspectroscopic studies of transitional nuclei with 50<N,Z<82 and on the basis of a quasi-particle-plus-triaxial rotor model. The isotope shift discrepancy observed is fairly well described by the droplet model.

Laser spectroscopic determination of the 50V quadrupole moment

Using the method of atomic-beam magnetic resonance, detected by laser-induced resonance fluorescence (ABMR-LIRF), the atomic ground-state hyperfine intervals of 50V were precisely measured. A quadrupole moment ratio Q( 50 V) / ( 51 V = −4.03(3) is obtained which results in Q( 50 V) = +0.21(4) b .

Reaction rates of NH 2-radicals with NO, NO 2, C 2H 2, C 2H 4 and other hydrocarbons

Absolute rate constants for gas phase reactions of NH2 radicals with nitrogen dioxide, nitric oxide, acetylene and ethylene have been determined in a discharge flow system with laser-induced resonance fluorescence detection of NH2. The radicals were produced by the fast reaction F+NH3. The kinetic measurements were performed in the temperature range 209≤T≤505 K at pressures of one torr He as the main carrier gas. The following rate constants were obtained: k N O 2 + N H 2 ( T ) = 1.9 ⋅ 10 20 ⋅ T − 3.0 [ c m 3 / mol sec ] k NO + N H 2 ( T ) = 2.7 ⋅ 10 17 ⋅ T − 1.85 [ c m 3 / mol sec ] k C 2 H 2 + N H 2 ( T ) = 1.42 ⋅ 10 16 ⋅ T − 2.7 [ c m 3 / mol sec ] The rate constant for the reaction of C2H4 with NH2 shows little temperature dependence kC2H4+NH2(T)=1.3·109 [cm3/mol sec]. The reactions of NH2 with allene and propylene are slow. The measurements lead to the upper limits kC3H4+NH2≤5·108 [cm3/mol sec] and kC3H6+NH2≤6·108 [cm3/mol sec] at room temperature.

Optical investigation of a gas-jet system

A new optical technique for visualization of low-density micro-jets is described which makes use of laser-induced resonance fluorescence. The technique is applied to the investigation of gas transport systems. Measurements of the spatial distribution of the gas jet and the aerosol beam are performed. It is demonstrated that decoupling and shaping of the aerosol beam is possible when capillaries with shaped nozzle ends are used. Aerosol beams with small divergence are achieved by Laval-type nozzles.

Spectroscopic observations of subsonic and sonic vapor flow inside an open-ended heat pipe

Spectroscopic measurements of the vapor flow velocities inside a heat-pipe oven have been performed as a function of pressure, heater power, and radial position inside the pipe. For this purpose the relative intensity of the collision-induced satellite lines in laser-induced resonance fluorescence spectra of the 7Li2 molecule has been employed. A one-dimensional flow model is presented which determines the vapor parameters as a function of position along the pipe. It predicts the onset of the sonic flow which has been verified experimentally. A criterion is derived from which the parameters of the vapor can be obtained from the ideal gas relation, neglecting velocity-dependent terms.

Matrix Isolation Laser Raman Spectroscopy. I. Vibrational Raman Spectra and Depolarization Measurements for Matrix Isolated Group IVa Dihalides, MX2 and MXY (where M = Ge, Sn, Pb and X, Y = Cl, Br), in Solid Argon and Nitrogen

The vibrational Raman spectra together with polarization data are reported for most of the monomeric dihalides MX2 and mixed dihalides MXY of Group IVa (where M = Ge, Sn, or Pb and X, Y = Cl or Br) isolated in both argon and nitrogen matrices at 4.2°K. Laser induced resonance fluorescence effects which interfere with gas phase Raman studies are eliminated in Raman studies of matrix isolated dihalides. The isotope components of ν1 and ν3 are clearly resolved in the case of PbCl2 in argon and assigned to Pb35Cl2, Pb35Cl37Cl, and Pb37Cl2. Diffusion controlled warmup data are recorded for all species in the temperature range 4.2–40°K. All isolated monomers were found to diffuse rapidly at 30–35°K and only in the case of GeCl2 was a definite, stepwise polymerization process observed. The final spectrum obtained by warming GeCl2 showed the presence of a polymeric structure containing both terminal and bridging chlorine atoms. The matrix Raman results demonstrate that spectral sensitivities and resolution can be achieved which are comparable with the complimentary matrix infrared data and that matrix Raman polarization measurements add a valuable new tool for matrix isolation studies.