Samuel M. Freund

Infra-red laser enhanced reactions: chemistry of vibrationally excited O3 with NO and O2(1Δ)

Abstract Vibrationally excited ozone, produced by absorption of CO2 laser radiation, was found to react significantly faster with NO and O2(1Δ) than thermal ozone. Using a modulation technique, absolute and relative rate constants at 300K for the following reactions were calculated assuming rapid equilibration between the three closely spaced vibrationally excited levels of O3, and that only the lowest level of these, the ν2 bending mode, is active in reaction. k1′ + k2′ = 2.7 × 10−13 cm3 molecule−1 s−1; (k1′ + k2′)/(k1 + k2) = 16.2 ± 4.0; k1′/k1 = 4.1 ± 2.0; k2′/k2 = 17.1 ± 4.3; k7′/k7 = 38 ± 20. These rate constants must be modified if a different combination of vibrationally excited levels is involved. The fraction of vibrational energy usable in chemical reaction was found to be about 15, 50 and ∼ 100% respectively for processes 1′, 2′ and 7′. Our measurements clearly differentiate between the participation of vibrational energy and thermal energy but do not distinguish differences between the individual vibrationally excited states. Details of the modulation technique, involving chemiluminescence detection of NO2 and resonance fluorescence detection of oxygen atoms, are described. Comparison of our results with a previous measurement of the summation reaction (1′ + 2′) shows excellent agreement.

Laser Stark measurements on OCS including the observation of zero-field-forbidden ΔJ = 0, ±2 transitions

Abstract Laser Stark measurements have been made on the 02 0 000 0 0 and 03 1 001 1 0 vibrational transitions of 16 O 12 C 32 S, 16 O 12 C 34 S, and 18 O 12 C 32 S, and on the 03 1 001 1 0 transition of 16 O 13 C 32 S, using a CO 2 laser. In addition to providing dipole moment information for excited vibrational states, these measurements give vibrational band centers accurate to several megahertz. To aid in optical pumping experiments, several near coincidences between CO 2 laser transitions and OCS absorption lines are discussed. Electric-field-allowed Δ J = 0 transitions are observed for the 2 ν 2 band of 16 O 12 C 32 S and 16 O 12 C 34 S, as well as Δ J = 2 transitions for the same band of 18 O 12 C 32 S.

Laser Stark spectroscopy of FCN

Abstract Using a CO 2 laser, Stark shifted resonances have been measured for the CF stretching fundamental ( ν 3 ) of FCN near 9.3 μm, and for two nearby “hot” bands. The band centers measured are 1076.492007 ± 0.000013 cm −1 for 00 0 1-00 0 0, 1085.741046 ± 0.000050 cm −1 for 01 1 1-01 1 0, and 1091.16222 ± 0.00015 cm −1 for 02 0 1-02 0 0. The ground state dipole moment of FCN is found to be 2.1203 ± 0.0010 D and dipole moments are also given for the other states observed. Values are given for the rotational constant and l -doubling constant for the 01 1 1 state.

Laser Stark spectroscopy of DCN and DC15N

Abstract Using a CO laser, laser Stark resonance spectra were measured for the CN stretching fundamentals (the 00 0 1-00 0 0 bands) of D 12 C 14 N and D 12 C 15 N near 1925 cm −1 . Laser Stark resonances were also measured for the hot band 01 1 1-01 1 0 of D 12 C 14 N. In addition to accurately determining the band centers, dipole moments are given for the different vibrational states involved.

Laser-induced photochemical enrichment of boron isotopes

A boron trichloride starting material containing both boron-10 isotopes andoron-11 isotopes is selectively enriched in one or the other of these isotopes by a laser-induced photochemical method involving the reaction of laser-excited boron trichloride with either H2 S or D2 S. The method is carried out by subjecting a low pressure gaseous mixture of boron trichloride starting material and the sulfide to infrared radiation from a carbon dioxide TE laser. The wave length of the radiation is selected so as to selectively excite one or the other of boron-10 BCl3 molecules or boron-11 BCl3 molecules, thereby making them preferentially more reactive with the sulfide. The laser-induced reaction produces both a boron-containing solid phase reaction product and a gaseous phase containing mostly unreacted BCl3 and small amounts of sulfhydroboranes. Pure boron trichloride selectively enriched in one of the isotopes is recovered as the primary product of the method from the gaseous phase by a multi-step recovery procedure. Pure boron trichloride enriched in the other isotope is recovered as a secondary product of the method by the subsequent chlorination of the solid phase reaction product followed by separation of BCl3 from the mixture of gaseous products resulting from the chlorination.

CO2 transverse excitation laser induced photochemical enrichment of carbon isotopes

CO2 transverse excitation laser photolysis of mixtures of Cl2CF2 with O2, NO, and Me2CCH2 is isotopically selective for carbon and experimental evidence indicates that the reaction may involve a laser produced difluorocarbene intermediate.

Isotopic enrichment in laser photochemistry

Laser technology has permitted more efficient study of the chemistry of molecules in excited states. The extent to which isotopic specificity is preserved in going from initial excitation to final product is a valuable diagnostic for excited state chemistry. This report summarizes initial results from several areas of investigation, each of which suggests that laser stimulation may offer more than simple rate enhancement.