Photolysis of CF3CH2CHO in the presence of O2 at 248 and 266 nm: quantum yields, products, and mechanism.

Three different detection techniques, coupled to pulsed laser photolysis (PLP), have been employed to determine the quantum yields of CF3CH2CHO at 248 and 266 nm: CF3CH2CHO + hν → CF3CH2 + HCO (R1a), CF3CH2CHO + hν → CF3CH3 + CO (R1b), and CF3CH2CHO + hν → CF3CH2O + H (R1c). (a) In the presence of air, Fourier transform infrared (FTIR) spectroscopy was employed at a total pressure of 760 Torr to monitor and quantify the loss of CF3CH2CHO at both wavelengths as well as the build-up of formed products (CO, CF3CH3, CF3CHO, and CF3CH2OH) after various laser pulses. Cyclohexane was added as OH-scavenger in most experiments. CF3CH3 was observed and quantified at both wavelengths, confirming that channel R1b is occurring. Small amounts of HCOOH and COF2 were also detected. (b) Time-resolved cw-cavity ring down spectroscopy (cw-CRDS) at 40 Torr He coupled to photolysis at 248 nm was employed for the detection of HO2 radicals. Varying the O2 concentration allows distinguishing the origin of the HO2 radicals from either R1a or R1c. OH radicals were simultaneously detected by laser-induced fluorescence. (c) Time-resolved tunable diode laser absorption spectroscopy (TDLAS) at 30 Torr N2 coupled to photolysis at 266 nm was employed for the determination of the quantum yields of CO. By varying the O2 concentration, a distinction can be achieved between the yields of prompt CO R1b or decomposition of highly excited CF3CH2CO from R1c and HCO radicals R1a. Channel R1a has been identified as the major reaction path. The overall quantum yield, Φλ(CF3CH2CHO), at 248 nm was found as Φ248nm = (0.76 ± 0.14) and (0.73 ± 0.20) from cw-CRDS and FTIR experiments, respectively. At 266 nm, the overall quantum yield was found as Φ266nm = (0.55 ± 0.10) and (0.47 ± 0.10) from TDLAS and FTIR experiments, respectively.

Rotational Spectrum of Vinylarsine.

The rotational spectrum of vinylarsine in the ground state has been studied in the range 7-320 GHz. The spectra of a syn conformer and a gauche conformer have been unambiguously assigned on the basis of the existence of a b-type or a c-type spectrum. Rotational constants, quartic, and some sextic centrifugal distortion constants were derived. For the syn form, measurements of low J aR0,1 transitions in a pulsed-nozzle Fourier transform microwave spectrometer (FTMWS) enabled the determination of the diagonal elements of the quadrupole tensor, as well as two spin-rotation constants. Ab initio calculations performed at the MP2 level using the 6-311++G(3df, 3pd) basis set reproduced experimental rotational constants within 0.2%. Copyright 1998 Academic Press.

Rotational Spectra of the Isotopic Species of Chloroform: Experimental and Ab Initio Structures.

The millimeter-wave spectra of three different samples of chloroform (CHCl3, CDCl3, and 13CHCl3) have been measured between 145 and 470 GHz which corresponds to J values between 22 and 70. We report accurate rotational and centrifugal distortion constants for the ground vibrational states of 11 isotopic species. The experimental ro, rs, rIepsilon, rrhom, and rz structures have been determined using the determined rotational constants. The structure has also been calculated ab initio at the SCF, MP2, RQCISD, and B3LYP levels using triple zeta polarized basis sets. The experimental results are found in excellent agreement with the ab initio predictions. An approximate equilibrium structure has been obtained by combining the experimental results and the ab initio calculations: re(C-H) = 1.080 (2) Å, re(C-Cl) = 1.760 (2) Å, and anglee(HCCl) = 108.23 (2) degrees. Copyright 1998 Academic Press.

Mid- and Near-Infrared Spectra, Millimeterwave Spectra, and Global Analysis of (16)O(12)C(80)Se.

We have recorded a total of 12 FTIR spectra of monoisotopic OC(80)Se in different spectral regions with a resolution (1/maximum optical path difference) between 2.7 and 13.2 x 10(-3) cm(-1). These spectra spanned the range from 350 to 7800 cm(-1), many bands being studied with different p x L products in order to also detect weak hot bands. Altogether 18 band systems comprising 81 different bands, mostly of Sigma type, were observed and analyzed by means of polynomial expansions in J(J + 1). New rotational transitions of vibrationally excited states as high as 2200 cm(-1) with J" 17-25 in the 140-210 GHz and J" 53-58 in the 430-470 GHz millimeterwave regions were measured with the assistance of predictions by the global fit. This fit was performed using a weighted least-squares procedure and employing the whole body of data, and about 100 molecular parameters were determined that describe the energy level of (16)O(12)C(80)Se with statistical accuracy. Improved highly accurate ground state parameters up to sextic centrifugal distortion terms were obtained by a merge of ground state combination differences and pure rotational data. The v(1), v(2), v(3) polyad interacts anharmonically with the v(1) - 1, v(2) + p, v(3) + q polyads with p + 2q = 4. Moreover, some local crossings with Coriolis interactions between (v(1), v(2), v(3)) and (v(1) - 1, v(2) + 3, v(3) + 1) levels were observed and treated perturbationally. Copyright 1999 Academic Press.