Table 1
IR band assignments and central wavelengths (μm) for the CH stretching modes in the conjugated cyclic molecules shown in Fig. 1.
| Origin → | sp2 | sp2 | sp3 | sp2 + sp3 | sp2 + sp3 | |||
|---|---|---|---|---|---|---|---|---|
| Aromatic | cis | Paired 2° CH2 | 2° CH2 | Paired | ||||
| Molecule | CH | -HC=CH-(a) | -CH2-CH2-(b) | =CH-CH2-HC=(c) | =CH-CH2-(d) | |||
| 1,3-Cyclohexadiene | 3.27 | 3.40 | 3.47 | 3.53 | ||||
| 1,4-Cyclohexadiene | 3.29 | 3.45 | 3.47 | 3.51 | ||||
| Cyclooctatetraene | 3.31 | |||||||
| Naphthalene | 3.26 | |||||||
| Anthracene | 3.28 | |||||||
| Phenanthrene | 3.32 | |||||||
| Pyrene | 3.28 | |||||||
| Average | 3.28 | 3.29 | 3.40 | 3.45 | 3.47 | 3.52 | ||
| ≍ Dispersion | ±0.02 | ±0.02 | ±0.01 | |||||
| IS, PDR & CS bands | 3.29 | 3.40 | 3.46 | 3.51 | ||||
| ≍Dispersion | ±0.01 | ±0.01 | ±0.02 | ±0.02 |
Notes. Found in: (a) in all three cycloalkenes, (b) only in 1,3-cyclohexadiene, (c) only in 1,4-cyclohexadiene, and (d) in 1,3- and 1,4-cyclohexadiene. See the main text for a justification of the band assignments, where aromatic and olefinic (sp2), and aliphatic (sp3) origins are indicated. All the tabulated bands are comparatively strong. The positions of the observed interstellar emission bands are also indicated; the larger uncertainties for the 3.46 and 3.51 μm bands reflect the difficulty in determining the band centre for these weaker and broader bands.
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