Effects of anharmonic splitting upon collisionless multiple-photon laser excitation of SF6

Qualitative agreement of the dependence of molecular excitation upon laser frequency, between non-perturbative quantum-mechanical calculations and experimental measurements of the collisionless multiple-photon excitation of a few vibrational quanta in SF₆ by a CO₂ laser, results when anharmonic splitting of the vibrational energy levels is taken into account.     

Identification of the SF6 transitions pumped by a CO2 laser

The quantum numbers (J values and octahedral symmetry types) of the SF₆ transitions from the ground state to v₃ = 1 that fall within ± 1.5 G Hz of the CO₂ P(14), P(18), and P(20) laser lines have been assigned. The SF₆ absorptions nearest these three laser frequencies are R(28) A⁰₂, P(33) A¹₂, and an F₂ component of P(59) or P(60), respectively.     

Multilevel,multifrequency laser pulse propagation

We give a nonperturbative method for calculating the complex index of refraction for each of several optical fields interacting with a multilevel system, and illustrate the method by calculating the gain and absorption on an optically pumped, nearly resonant Raman transition as functions of the laser frequencies and fields, including the effects of dephasing and incoherent pumping of populations.     

Towards an explanation of collisionless multiple-photon laser dissociation of SF6

The rapidity and high degree of molecular vibrational excitation by the absorption of ir laser light in SF₆ and other molecules may be due in large part to the anharmonic splitting of excited vibrational states. Anharmonic splitting of an overtone or combination vibrational level (i) is possible only in molecules with degenerate vibrational states, (ii) can be comparable in magnitude to the net anharmonic shift of the level, (iii) is generally much larger than the rotational shifts which have previously been proposed as an explanation for the dissociation of SF₆. We find that consecutive nearly resonant transitions are possible in SF₆ up to υ₃ = 5 to 10.     

Further studies on the synthesis of α-fluoro carbonyl compounds [1]

The trimethylsilyl enol ethers of cycloalkanones and acid esters are converted in high yields (70–90%) to the corresponding α-fluoro carbonyl derivative using XeF₂ in CH₂Cl₂. Non-cyclic α-hydroxy ketones such as ethyl mandelate are efficiently transformed to the α-fluoro product by DAST and by Ishikawa's reagent. Nucleophilic displacement of halogen by fluoride failed in cyclic systems, giving instead, α,β-unsaturated ketones in DMF or CH₃CN (18-crown-6) and 1,2-diones in DMSO, with KF acting as a base. Attempts at DMSO oxidation of I(Br)F adducts failed to give the α-fluoro ketones, but resulted in dehydrohalogenation to the $\text{trans}$-vinyl fluorides.     

Essential Oil Composition and Bioactivity of Two Juniper Species from Bulgaria and Slovakia

Juniperus excelsa M. Bieb and J. sabina L. contain essential oil (EO), while J. sabina also contains podophyllotoxin, which is used as a precursor for anti-cancer drugs. Two studies were conducted. The first assessed the variability in the EO profile and podophyllotoxin concentration of the two junipers, depending on the location and tree gender. The main EO constituents of J. excelsa were α-cedrol, α-limonene and α-pinene, while the constituents in J. sabina were sabinene, terpinen-4-ol, myrtenyl acetate and α-cadinol. The podophyllotoxin yield of 18 J. sabina accessions was 0.07–0.32% (w/w), but this was not found in any of the J. excelsa accessions. The second study assessed the effect of hydrodistillation (Clevenger apparatus) and steam distillation (in a semi-commercial apparatus) on the EO profile and bioactivity. The extraction type did not significantly alter the EO composition. The EO profiles of the two junipers and their accessions were different and may be of interest to the industry utilizing juniper leaf EO. Breeding and selection programs could be developed with the two junipers (protected species) in order to identify chemotypes with (1) a high EO content and desirable composition, and (2) a high concentration of podophyllotoxin in J. sabina. Such chemotypes could be established as agricultural crops for the commercial production of podophyllotoxin and EO.