A portion of the molecular iodine LIF spectrum generated from excitation at 514.5 nm. (a) The primary emission peaks arising from 43–6 relaxation. The triplet structure is due to the pair of overlapping rotational doublets. (b) The spectrum is enhanced ×20 to show emission peaks from excited states populated by collisions, and also a 58–7 emission peak.
(a) The optical path for simultaneous collection of a Raman signal and a molecular iodine LIF reference signal. (b) Side view of the optics at the entrance slits to the polychromator showing the spatial separation of the Raman signal and LIF reference signal.
Simultaneously collected liquid cyclohexane Raman spectrum and molecular iodine reference spectrum. (a) A portion of the CCD image. The cyclohexane spectrum is in the top region of the image, and the LIF spectrum is in the bottom region. The complete image is wider and includes the 43–3 LIF triplet. (b) The cyclohexane spectrum generated from a horizontal cross section of the top region of the CCD image. (c) The LIF spectrum generated from a horizontal cross section of the bottom region of the CCD image.
A representative graph of residuals when the pixel coordinates of molecular iodine LIF peaks are fit to literature energy values in vacuum wavenumbers using a three-parameter optomechanical model [Eq. (6)]. Large circles: primary 43–4, 43–5, and 43–6 emission triplets. Triangle: 58–7 emission peak. Small circles: secondary calibration peaks from excited states populated by collisions. See also Figs. 1 and 3(c). Note that the direction of the pixel (energy) axis in Fig. 4 is reversed compared to the absolute wavenumber axis of Fig. 1.
Spectral coverage map of molecular iodine LIF peaks from −400 to that may serve as calibration points for instruments with resolution on the order of . Each row of data points spans : the top row is from 3600 to . Vacuum wavenumber shifts are relative to the 514.5-nm laser line. Large circles: primary emission triplets. The values of are shown below the circles. Triangles: emission peaks. Diamond: 514.5-nm laser line. Small circles: secondary calibration peaks from excited states populated by collisions. Alternate versions of this figure expressed in units of absolute vacuum wavenumber and wavelength in air are available in the supplementary material (Ref. 40).
(a) The 43–17 molecular iodine LIF spectrum at resolutions of 1.0 and . (b) Shift in the LIF peak maximum relative to the location of the branch [the , peak] as a function of instrumental resolution. Open circles: 43–1 emission. Black triangles: 43–17 emission.
Raman spectrum of the 1–0 -branch from atmospheric nitrogen gas. Open circles: experimental measurements. Vertical lines: calculated -branch rotational line structure. Fit line: convolution of calculated -branch rotational lines with a Gaussian approximation of the instrumental response function.
Residual differences between experimental and literature laser line energies (Ref. 21) following CCD image calibration using LIF spectra.
Cyclohexane peak locations from this work compared with literature values. Vacuum wavenumber shifts found in this work were converted to values in air at and 1 atm. Locations of peak maxima were determined at the instrumental resolution of , and again after artificially convoluting the data with Gaussian peaks of 3.2 and FWHM.
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