No abstract

The rotational structure in the C-type bands of the high-resolution (0.002 cm-1), gas-phase infrared spectra of four isotopomers of trans-1,2-dichloroethylene has been analyzed. The C-type band, which is due to CH or CD out-of-plane flapping, is at 897.949 82 (3) cm-1 for the normal species with 35Cl2. For the 35Cl2 variants, the ground-state rotational constants in cm-1 are A = 1.747 268 (3), B = 0.051 570 5 (3), and C = 0.050 080 7 (3) for the normal species; A = 1.677 033 (2), B = 0.051 501 0 (2), and C = 0.049 954 0 (2) for the 13C2 species; and A = 1.181 144 7 (9), B = 0.051 540 7 (2), and C = 0.049 371 9 (2) for the d2 species. For the d 2-35Cl37Cl isotopomer, A = 1.180 765 (2), B = 0.050 164 9 (3), and C = 0.048 107 5 (3) cm-1. A substitution structure (r s) was fit and found to have r CH = 1.078 (4) Å, r CC = 1.305 (5) Å, r CCl = 1.740 (3) Å, αCCH = 125.3 (5) Å, and αCCl = 119.9 (4) Å. Structural adjustments in going from the lower energy cis isomer to the higher energy trans isomer are discussed in the context of current qualitative theories of the cis effect.