C2H2 vibration-rotation bands

Other sources of data have generally been of much less use for anhar-monic force field studies than high-resolution infrared and microwave measurements. Solid-state infrared measurements using the matrix-isolation technique have recently provided useful vibrational data for some species inaccessible to gas-phase measurements, e.g., the cyanate (OCN )14 ls and nitrate (NO3)16 anions. Gas-phase Raman measurements of vibration/rotation bands are very difficult to perform with adequate resolution, and Raman data have mainly been utilized for locating some of the infrared-inactive fundamentals in symmetrical molecules such as C02, CS2,17 C2H2,18 CH4,19 20 C. 21"23 High-resolu-... 

Fig. 3.4.6 The V5 vibration-rotation band of acetylene (C2H2) recorded at high spectral resolution (0.003 cm ). The P-, Q-, and R-branches are indicated, and the lower-state J value is shown for lines in the P- and R-branches. The sample was in a 1 cm cell at 0.162 mbar and 296 K. Structure in the continuum level is due to variations in the response of the spectrometer. Lines of CO2 in the optical path appear in the 666-690 cm region.

In this experiment, several vibrational-rotational infrared bands of C2H2 and C2D2 will be recorded at medium to high resolution ( 1 cm ). These spectra will be analyzed to extract rotational constants for use in the calculation of accurate values for the C—H and C—C bond lengths. The role of symmetry and nuclear spin in determining the activities... 

Figure 0.2 Direct overtone spectroscopy of C2H2 using Fourier transform spectroscopy. Here, at high resolution, the entire band of rotational transitions, which accompany a given vibrational transition, can be resolved. Here the band, in the visible range, corresponding to the direct excitation of v = 5 of the v3 stretch mode is shown. (Adapted from Herman et al., 1991. See also Scherer, Lehmann, and Klemperer, 1983, and Figure 8.4.)...

Rotational and vibrational distributions, as well as relative intensities of bands emitted by different molecules, have been surveyed by Krishnamachari and Broida272. They worked with 0 + C2H2 and also studied effects of added 02. 

Figure 4.3-7 Rotation-vibration spectrum of C2H2 (5 hPa, 25 °C, l(i cm) at a spectral resolution of 0,05 cm with the inset the intensity alternation due to spin statistics in the /5-fundamenlal is illustrated (the underlying fine structure is from a hot band transition with its 0-branch shifted to lower wavenumbers compared to the fundamental).

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