Dennis W. Tokaryk

Testing for fullerenes in geologic materials: Oklo carbonaceous substances, Karelian shungites, Sudbury Black Tuff

Fullerenes have been reported from diverse geologic environments since their discovery in shungite from Karelian Russia. Our investigation is prompted by the presence of onionskin-like structures in some carbonaceous substances associated with the fossil nuclear fission reactors of Oklo, Gabon. The same series of extractions and the same instrumental techniques, laser desorption ionization and high-resolution mass spectroscopy (electron-impact mass spectroscopy), were employed to test for fullerenes in samples from three different localities: two sites containing putative fullerenes (Sudbury Basin and Russian Karelia) and one new location (Oklo, Gabon). We confirm the presence of fullerenes (C 6 0 and C 7 0 ) in the Black Tuff of the Onaping Formation impact breccia in the Sudbury Basin, but we find no evidence of fullerenes in shungite samples from various locations in Russian Karelia. Analysis of carbonaceous substances associated with the natural nuclear fission reactors of Oklo yields no definitive signals for fullerenes. If fullerenes were produced during sustained nuclear fission at Oklo, then they are present below the detection limit (∼100 fmol), or they have destabilized since formation. Contrary to some expectations, geologic occurrences of fullerenes are not commonplace.

Experimental determination of a spin-orbit interval in the C″Πui5 state of N214

We have developed an experimental setup using the combination of laser optogalvanic detection and a supersonic expansion of excited N2 to record the high resolution spectrum of the (3-1) and (4-2) Herman infrared bands (C″Πui5−A′Σg+5). We report the first experimental determination of a spin-orbit interval (about 24cm−1) in the C″Πui5 state of N2 for both the (3-1) and (4-2) vibrational bands as well as the first observation of the v′=4 vibrational level.

The spin-orbit and rotational constants for the N2 C″Πui5(v=3) state

The spin-orbit (A=−16.4cm−1) and rotational (B=1.017cm−1) constants for the N2 C″Πui5(v=3) level are determined by a fit to rotational lines in the C″Πu5−A′Σg+5(3-1) band that terminate in JΩ′′=33, 43, 32, and 42 levels of the C″ state. The C″-state spin-orbit constant is consistent with semi-empirical estimates, based on spin-orbit constants observed in several other electronic states of N2 and the atomic spin-orbit coupling constant, ζ(N2p). The C″–A′ bands exhibit the unusual feature of oppositely degraded sub-band heads, Ω′=3 (red) and Ω′=1, 0, and −1 (blue). The unusually wide range of BΩeff values, from 0.85cm−1 (Ω=3) to 1.28cm−1 (Ω=−1) for C″Π5(v=3) should be diagnostically useful for Ω′-assignments. The C″Π5(v=3) level lies 14257.17 and 90599cm−1 above A′Σg+5(v=1) and XΣg+1(v=0), respectively, and Re(C″Π5)=1.50A.

Optogalvanic spectroscopy of the C″Πui5−A′Σg+5 electronic system of N2

We have recorded spectra involving the 3-1, 4-2, 2-0, and 2-2 bands of the C″Πui5−A′Σg+5 electronic system of N2 using optogalvanic detection in a discharge through a supersonic jet expansion of argon mixed with a trace of nitrogen gas. The spectra have an effective rotational temperature of about 45K. They involve all five spin-orbit components of the C″Πui5 state, which has allowed for precise determination of the spin-orbit coupling in this state. Analysis of the C″Πui5 state Λ-doubling shows that it is caused primarily by a first-order spin-spin effect rather than by interaction with Σu± states. Our results allow us to assign lines in the 4-2 and 2-0 bands observed in a fluorescence depletion experiment conducted over ten years ago [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 103, 9929 (1995)], and to comment on the suggestion that perturbations to the CΠu3 v=1 level of N2 arise from interactions with the C″Πui5 state.We have recorded spectra involving the 3-1, 4-2, 2-0, and 2-2 bands of the C″Πui5−A′Σg+5 electronic system of N2 using optogalvanic detection in a discharge through a supersonic jet expansion of argon mixed with a trace of nitrogen gas. The spectra have an effective rotational temperature of about 45K. They involve all five spin-orbit components of the C″Πui5 state, which has allowed for precise determination of the spin-orbit coupling in this state. Analysis of the C″Πui5 state Λ-doubling shows that it is caused primarily by a first-order spin-spin effect rather than by interaction with Σu± states. Our results allow us to assign lines in the 4-2 and 2-0 bands observed in a fluorescence depletion experiment conducted over ten years ago [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 103, 9929 (1995)], and to comment on the suggestion that perturbations to the CΠu3 v=1 level of N2 arise from interactions with the C″Πui5 state.

A laser spectroscopic study of the X̃Πg2,ÃΠu2, and B̃Σu+2 states of BS2: Renner–Teller, spin-orbit, and K-resonance effects

The lowest-lying vibronic levels of the X,A, and B states of BS2 have been investigated at high resolution using a combination of room-temperature absorption and supersonic jet data. In both cases, the BS2 radical was prepared in an electric discharge using a precursor gas mixture of BCl3,CS2, and either helium or argon. Extensive absorption spectra were obtained for the 000 and 211 bands of the AΠu2-XΠg2 electronic transition in the visible. The A-X211 and BΣu+2-XΠg2211 bands of jet-cooled BS2 were also studied with laser-induced fluorescence techniques. By fitting the 000 bands of both electronic transitions simultaneously, we were able to precisely determine the spin-orbit splittings in both the A and X states. Similarly, the 211 bands were fitted in a merged analysis in order to determine the relative separations of the vibronic components of the ground and first excited state bending levels as accurately as possible. Due to a large spin-orbit splitting and small Renner–Teller interaction, ...

Far-infrared spectrum of S(CN)2 measured with synchrotron radiation: global analysis of the available high-resolution spectroscopic data.

The high resolution Fourier transform spectrum of the chemically challenging sulfur dicyanide, S(CN)2, molecule was recorded at the far-infrared beamline of the synchrotron at the Canadian Light Source. The spectrum covered 50-350 cm(-1), and transitions in three fundamentals, ν4, ν7, and ν8, as well as in the hot-band sequence (n + 1)ν4 - nν4, n = 1-4, have been assigned and measured. Global analysis of over 21,300 pure rotation and rotation vibration transitions allowed determination of precise energies for 12 of the lowest vibrationally excited states of S(CN)2, including the five lowest fundamentals. These results constitute an extensive set of benchmarks for ab initio anharmonic force field calculations and the observed and calculated vibration-rotation constants and anharmonic frequencies are compared. The semiexperimental equilibrium, r(e)(SE), geometry of S(CN)2 has also been evaluated. In the course of the measurements, new information concerning the physical chemistry of S(CN)2 has been obtained.

Resolved fluorescence spectra of NiH. Electronic structure, electronic energy transfer, and the Zeeman effect in low-lying states

Fourier transform spectra of collisionally induced fluorescence following isotopically selective laser excitation of NiH at ∼550 nm have located an excited Ω = 1/2 state of NiH lying 17900 cm−1 above the electronic ground state. This is identified as v = 0 of a 2Π1/2 state originating from an Ni+ 3d84s1 2F configuration. Emission from this Ω′ = 1/2 state occurs predominantly to v″ = 0 and 1 of the 2Σ+ and W2 2Π1/2 ligand field states, locating elusive f parity levels of W2 2Π1/2 up to 5600 cm−1 above the first rotational level of the electronic ground state, X 1 2Δ5/2. Collisionally induced fluorescence following laser excitation at lower energies has also been recorded in the presence of a magnetic field (0.7–1 T), at Doppler limited resolution. Effective Landé factors g J for rotational levels of the v = 0 and 1 levels of the low-lying Ω″ = 5/2 and 3/2 components of the 2Δ and 2Π states of NiH have been derived from partially resolved Zeeman patterns. About 1600 transitions recorded in field-free conditions have been reduced to term energies relative to the lowest level of the ground state. They confirm strong spin-orbit mixing between the low-lying ligand-field states.

FOURIER TRANSFORM ABSORPTION SPECTROSCOPY OF C3 IN THE ν3 ANTISYMMETRIC STRETCH MODE REGION

The C3 molecule has been detected in a variety of astrophysical objects thanks to the well-known 4050 Å (AΠu– XΣg ) electronic transition as well as the two IR active modes of the electronic ground state: ν2 (∼ 63.42 cm−1) and ν3 (∼ 2040.02 cm−1)b. Previous laboratory data in the ν3 region, obtained using diode laser spectroscopy and the photolysis of allene to produce C3, permitted measurement of the fundamental (0,0,1)Σ–(0,0,0)Σ as well as the hot bands: (0,1,1)Π– (0,1,0)Π; (0,2,1)Σ–(0,2,0)Σ; (0,2,1)∆–(0,2,0)∆ and provided insights on the anharmonicity of the (0,nν2,1) vibrational patternc. We have recorded the absorption spectrum of C3 in the 1800–2100 cm−1 region (at a resolution of 0.003 cm−1) using the Bruker IFS 125 Fourier Transform spectrometer at the AILES beamline of Synchrotron SOLEIL. C3 was produced in a DC discharge of methane heavily diluted in helium. The rovibrational temperature of C3 produced in our discharge is noticeably higher than in Ref. [4], which allowed us to extend measurements to higher J values. More interestingly, we assigned new hot bands involving higher quanta of the ν2 bending states: (0,nν2,1) with n ranging from 0 to 5. Despite the absence of Q branches for these bands, which results in a possible ambiguous J-assignment of P and R lines, the large variety of data considered in this work, in addition to our experimental data and including observations of comet spectra, allows confident assignments.

A CRDS sputter-source experiment to study MH radicals: application to NiH and NiD

ABSTRACT Signatures of metal hydride molecules appear in the optical spectra of cool stars. The observed spectra are used not only for identification of the molecule, but also to assess the abundance of the metal from which the molecule is composed, and to measure the strength of the magnetic field in which the molecule is immersed through the Zeeman splitting of individual spectral lines. Metal hydrides are short-lived radicals, often produced via an electrical discharge, and their steady-state concentrations in a sample are low. High-sensitivity probing techniques, like laser-induced fluorescence, are often appropriate, but (typically much less sensitive) absorption techniques are more useful to assess metal abundances. We describe here a cavity ring-down spectroscopy experiment, usually used to detect absorptions from stable molecules, to collect spectra with very high sensitivity and reproducibility from prototypical metal hydrides NiH and NiD. We have constructed an optical cavity of high finesse (F = 60,000) into which a sputtering source is inserted, and have employed optical fibre and a rigid mounting scheme to keep the ring-down mirrors in alignment during an experiment and between days. We compare our NiH/NiD absorption data with literature results, and highlight some of the strengths and weaknesses of this approach.

Spectroscopy of the X1Σ+, a1π and B1Σ+ electronic states of mgs

The spectra of some astrophysical sources contain signatures from molecules containing magnesium or sulphur atoms. Therefore, we have extended previous studies of the diatomic molecule MgS, which is a possible candidate for astrophysical detection. Microwave spectra of XΣ , the ground electronic state, were reported in 1989a and 1997b, and the BΣ–XΣ electronic absorption spectrum in the blue was last studied in 1970c. We have investigated the BΣ–XΣ 0-0 spectrum of MgS at high resolution under jet-cooled conditions in a laser-ablation molecular source, and have obtained laser-induced fluorescence spectra from four isotopologues. Dispersed fluorescence from this source identified the lowlying AΠ state near 4520 cm−1. We also created MgS in a Broida oven, with the help of a stream of activated nitrogen, and took rotationally resolved dispersed fluorescence spectra of the BΣ–AΠ transition with a grating spectrometer by laser excitation of individual rotational levels of the BΣ state via the BΣ–XΣ transition. These spectra provide a first observation and analysis of the AΠ state.