Jet-cooled laser spectroscopy of the cyclohexoxy radical

The laser-induced fluorescence and laser-excited dispersed fluorescence spectra of the cyclohexoxy radical has been observed under two sets of free-jet-cooling conditions, characterized by rotational temperatures of approximately 1 and 100 K. Although five conformers of cyclohexoxy are possible, it appears that all presently observed spectral bands can be accounted for by a single one. All cold spectral bands are assigned to the B-X electronic transition of the cyclohexoxy radical. Transitions to both a' and a" B state vibrational levels are observed and allowed due to a substantial pseudo-Jahn-Teller effect in the X state. Hot bands are also observed, which we attributed to transitions to the B state from the low-lying A electronic state. Analysis of the spectra yields vibrational frequencies for the X, A, and B states as well as the energy separations of their vibrationless levels.     

Double pulse laser ablation and laser induced breakdown spectroscopy: A modeling investigation

A numerical model, describing laser–solid interaction (i.e., metal target heating, melting and vaporization), vapor plume expansion, plasma formation and laser–plasma interaction, is applied to describe the effects of double pulse (DP) laser ablation and laser induced breakdown spectroscopy (LIBS). Because the model is limited to plume expansion times in the order of (a few) 100 ns in order to produce realistic results, the interpulse delay times are varied between 10 and 100 ns, and the results are compared to the behavior of a single pulse (SP) with the same total energy. It is found that the surface temperature at the maximum is a bit lower in the DP configuration, because of the lower irradiance of one laser pulse, but it remains high during a longer time, because it rises again upon the second laser pulse. Consequently, the target remains for a longer time in the molten state, which suggests that laser ablation in the DP configuration might be more efficient, through the mechanism of splashing of the molten target. The total laser absorption in the plasma is also calculated to be clearly lower in the DP configuration, so that more laser energy can reach the target and give rise to laser ablation. Finally, it is observed that the plume expansion dynamics is characterized by two separate waves, the first one originating from the first laser pulse, and the second (higher) one as a result of the second laser pulse. Initially, the plasma temperature and electron density are somewhat lower than in the SP case, due to the lower energy of one laser pulse. However, they rise again upon the second laser pulse, and after 200 ns, they are therefore somewhat higher than in the SP case. This is especially true for the longer interpulse delay times, and it is expected that these trends will be continued for longer delay times in the μs-range, which are most typically used in DP LIBS, resulting in more intense emission intensities.     

Near-infrared laser spectroscopy of NiI

Laser-induced fluorescence spectrum of NiI in the near infrared region of 714-770 nm has been recorded. Seven bands belonging to three electronic transition systems were observed and analyzed: the (0,0), (1,0), and (2,0) bands of [13.3] (2)Sigma(+)-A (2)Pi(3/2) system; the (1,1) and (0,1) bands of [13.9] (2)Pi(3/2)-X (2)Delta(5/2) system; and the (0,0) and (1,0) bands of [13.9] (2)Pi(3/2)-A (2)Pi(3/2) system. Spectra of isotopic molecules confirmed the vibrational quantum number assignment of the observed bands. Least-squares fit of rotationally resolved transition lines yielded accurate molecular constants for the v=0-2 levels of the [13.3] (2)Sigma(+) state, the v=0 level of the A (2)Pi(3/2), and the v=1 level of the X (2)Delta(5/2) state. The vibrational separation, DeltaG(1/2), of the ground state was measured to be 276.674 cm(-1). With the observation of the [13.9] (2)Pi(3/2)-A (2)Pi(3/2) and [13.9] (2)Pi(3/2)-X (2)Delta(5/2) transitions, we accurately determined the energy separation between the A (2)Pi(3/2) and the X (2)Delta(5/2) to be 163.847 cm(-1). This confirms that the order of the A (2)Pi(3/2) and X (2)Delta(5/2) states in NiI is reversed when compared with other nickel monohalides.     

Imaged intracavity laser absorption spectroscopy

Using a laser resonator design which supports many high order transverse modes it is possible to enhance a spatial variation (i.e., an image) as well as a spectral variation in absorption of a sample inside the optical cavity of an organic dye laser. This technique also enhances the practical sensitivity of intracavity absorption spectroscopy.     

Fluorescence spectroscopy of laser vaporized species

The plasma produced by a Nd-Yag laser above a metal surface is measured by time resolved optical spectroscopy. The emission of atoms, ions and diatomics is observed for silver, copper and molybdenum. (Cu₂, ωe=263.3 cm^?1 X-state, 189.8 cm^?1 A-state). From these small species clusters are formed with a size distribution between 10 and 80 Å diameter measured by electron microscopy.     

Infrared laser spectroscopy of jet-cooled cyclopropane

The v₁₁ band of cyclopropane between 850 and 880 cm^?1 has been recorded in a molecular beam source using a tunable infrared diode laser. The beam from a 50 μm nozzle was chopped at about 1 kHz and the absorption synchronously detected. Preliminary analysis yields a value of 868.357(1) cm^?1 for the band centre.     

Infrared laser spectroscopy of SH+

Many components of the fundamental band of ³²SH⁺ have been detected and measured in absorption using infrared diode laser spectroscopy. The transitions are characterized by the triplet fine-structure splitting expected for the X ³∑⁻ state of the cation and their positions are in good agreement with predictions obtained from an analysis of the A ³Π-X ³∑⁻ system. Some lines with opposite phase to the cation signals are tentatively assigned to SH⁻.     

Mass-resolved laser ionization spectroscopy of HCl

We report 2 + 1 resonantly enhanced multiphoton ionization spectra of HCl between 82000 and 89000 cm⁻¹ two-photon energy with mass resolution of the ions. We see significant production of atomic products subsequently ionized when the two-photonresonant state has a long bond length but we see only HCl⁺ when the resonant state is of Rydberg origin (and hence has a short bond length). The state at 82780 cm⁻¹, assigned as the E¹Σ⁺(ν = 0) state, exhibits the production of atoms that is characteristic of a state with a long bond length, evidence that this state should be incorporated into the double-minimum B¹Σ ⁺ state.     

High-resolution laser excitation spectroscopy of the A2E-X2A1 transition of SrCH3

High-resolution laser excitation spectroscopy has been used to record the A (2)E-X (2)A(1) electronic transition of SrCH(3) in a laser ablation/molecular jet source. Transitions arising from the K(')=1<--K(")=0, K(')=0<--K(")=1, and K(')=2<--K(")=1 subbands have been observed and assigned. The data were modeled with (2)E and (2)A(1) symmetric top Hamiltonian matrices in a Hund's case (a) basis, using a least squares fitting program. Rotational and fine structure parameters for the A (2)E state were determined. A comparison of the spin-orbit energy separation in the A (2)E state to other strontium containing free radicals showed that the Jahn-Teller effect is negligible. The spin-rotation constants for the A (2)E state were calculated using the pure precession model and were found to be in good agreement with the experimentally determined parameters. These calculations suggest that the A (2)E state of SrCH(3) is not entirely of p orbital character. The rotational constants were used to estimate the structural parameters of SrCH(3) in the A (2)E state. The strontium-carbon bond length was found to decrease by approximately 0.006 A, and the hydrogen-carbon-hydrogen bond angle opened by approximately 0.8 degrees compared to the X (2)A(1) state, similar to the geometry changes observed for CaCH(3).     

Submillimetre laser and interferometric spectroscopy of the alkyl alcohols

The far-infrared power absorption of a series of alkyl alcohols has been measured with interferometry and laser spectroscopy. The two techniques are complementary and in good agreement. The vibrational COH torsion and O...H stretch have been analysed, particularly for methanol in dilute solutions.     

A comparison of laser ablation inductively coupled plasma mass spectrometry,micro X-ray fluorescence spectroscopy,and laser induced breakdown spectroscopy for the discrimination of automotive glass

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), micro X-ray fluorescence spectroscopy (μXRF), and laser induced breakdown spectroscopy (LIBS) are compared in terms of discrimination power for a glass sample set consisting of 41 fragments. Excellent discrimination results (> 99% discrimination) were obtained for each of the methods. In addition, all three analytical methods produced very similar discrimination results in terms of the number of pairs found to be indistinguishable. The small number of indistinguishable pairs that were identified all originated from the same vehicle. The results also show a strong correlation between the data generated from the use of µXRF and LA-ICP-MS, when comparing µXRF strontium intensities to LA-ICP-MS strontium concentrations. A 266 nm laser was utilized for all LIBS analyses, which provided excellent precision (< 10% RSD for all elements and < 10% RSD for all ratios, N = 5). The paper also presents a thorough data analysis review for forensic glass examinations by LIBS and suggests several element ratios that provide accurate discrimination results related to the LIBS system used for this study. Different combinations of 10 ratios were used for discrimination, all of which assisted with eliminating Type I errors (false exclusions) and reducing Type II errors (false inclusions). The results demonstrate that the LIBS experimental setup described, when combined with a comprehensive data analysis protocol, provides comparable discrimination when compared to LA-ICP-MS and μXRF for the application of forensic glass examinations. Given the many advantages that LIBS offers, most notably reduced complexity and reduced cost of the instrumentation, LIBS is a viable alternative to LA-ICP-MS and μXRF for use in the forensic laboratory.     

Diode laser cavity ring down spectroscopy

We recently demonstrated how in cativy ring down spectroscopy (CRDS) a CW single frequency dye laser may be conveniently employed in place of the pulsed laser of standard CRDS. Here we extend this result to external cavity tunable diode lasers. Compact spectroscopic devices with extreme sensitivity (2 × 10⁻¹⁰/cm) become a reality. To demonstrate the instrumental resolution we obtained high quality NO₂ spectra in a supersonic slit jet, with a residual Doppler width of about 250 MHz.     

Applications of laser spectroscopy in polymer science

Applications of Rayleigh, Brillouin and Raman spectroscopy in polymer science are outlined. Since the advent of the laser and the new optical technology that it has spawned, new uses of light scattering have developed, particularly in the determination of dynamic properties of materials. The formalism of time correlation functions best describes the evolution of these microscopic processes. The physical basis of the three major light-scattering spectroscopies is first discussed within this general theoretical framework. A selection of practical applications will then be discussed that includes information obtainable about local polymer chain motion, large-scale diffusion, relaxation behavior, phase transitions and ordered states of macromolecules.     

Near-infrared diode laser spectroscopy of free radicals

Spectroscopic results on the radicals HCSi, CCO, and FeC obtained by studying in detail energy level structures using 0.8 microm diode laser system are reported. Of these radicals, the CCO radical was investigated mainly using Fabry-Perot type diode lasers with inconvenient mode gaps in the early stage of our near-infrared diode laser spectroscopic study of free radicals, and on the other hand, the FeC and HCSi radicals were studied using an external cavity diode laser. For the FeC radical, which is an interesting radical composed of an iron atom having 3d electrons, information on spin-orbit interaction between the triplet electronic ground state and a low-lying singlet electronic excited state is reported somewhat in detail. For the HCSi and CCO radicals, spectral particularities produced by a Renner-Teller interaction and a spin-orbit interaction are described for their high-resolution spectroscopic interest.     

Quantum limited frequency modulation laser spectroscopy

Frequency modulation spectroscopy (FMS) is an optical heterodyne technique which allows high-resolution, high-sensitivity measurements of absorptions or dispersions associated with narrow spectral features. With new methods, the sensitivity limitations of FMS (caused by residual amplitude modulation) can be overcome, and quantum-limited performance can be readily achieved.