We measured at 296 K the rotational line strengths and pressure-broadening coefficients for the 1.27-mum, a (1)D(g)-X (3)?(g)(-), v = 0-0 band of O(2) with a Fourier transform infrared spectrometer using an optical path length of 84 m, a spectral resolution of 0.01 cm(-1), and sample pressures between 13 and 104 kPa. The integrated band strength is 7.79(17) x 10(-6) m(-2) Pa(-1) [7.89(17) x 10(-5) cm(-2) atm(-1)], and the Einstein Acoefficient for spontaneous emission is 2.237(51) x 10(-4) s(-1), which corresponds to an upper-state1/e lifetime of 1.24(3) h. The pressure-broadening coefficients decrease with increasing N and range from 19 to 38 MHz/kPa (FWHM). The mean value for the transitions studied is 30.3(21) MHz/kPa [0.1024(71) cm(-1)/atm] (FWHM). The Einstein A coefficient determined here is in good agreement with the widely accepted value of 2.58 x 10(-4) s(-1) initially obtained by Badgeret al. [J. Chem. Phys. 43, 4345 (1965)] more than 30 years ago. The standard uncertainties given above are one standard deviation.

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The rotational spectra of 7 of the expected 13 conformational isomers of 1-hexene have been measured and assigned at a rotational temperature of <2 K using a pulsed-molecular-beam Fourier transform microwave spectrometer. The rotational assignments were guided by predictions from the MM3 molecular mechanics force field of Allinger et al. and by ab initio electronic-structure calculations (MP2/6-31G*). Six of the seven observed conformers have C 1 symmetry, as verified by the observation of a-, b-, and c-type electric-dipole transitions. The remaining conformer has C s symmetry, consistent with its small inertial defect, Δ ≡ I cc − I bb − I aa = −12.65 uÅ2, and the observation of only a and b-type transitions. Here, I αα is the moment of inertia of the conformer about its α-principal axis. The inertial defects determined for the seven conformers range from −12.65 to −51.29 uÅ2. Both the molecular mechanics and ab initio calculations indicate the observed conformers are associated with the seven lowest-energy conformational minima of 1-hexene. The ab initio calculated energy difference between the lowest and highest energy conformers observed is 326 cm-1, including vibrational zero-point contributions, indicating that the conformational temperature is not equilibrated with the <2 K rotational temperature of the molecular-beam expansion.