A complete structure of trans-1,2-dichloroethylene from high-resolution infrared spectroscopy

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 Cl-35(2). For the Cl-35(2) 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 C-13(2) species; and A = 1.181 144 7 (9), B = 0.051 540 7 (2), and C = 0.049 371 9 (2) for the d(2) species. For the d(2)-(SClCl)-S-35-Cl-37 isotopomer, A = 1.180 765 (2), B = 0.050 164 9 (3), and C = 0.048 207 5 (3) cm(-1). A substitution structure (r(s)) was fit and found to have r(CH) = 1.078 (4) Angstrom, r(CC) = 1.305 (5) Angstrom, r(CCl) = 1.740 (3) Angstrom, alpha(CCH) = 125.3 (5) Angstrom, and alpha(CCl) = 119.9 (4) Angstrom. 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.