Knowledge Bank

($Z$)- and ($E$)-Ethanethial S-oxide, geometrical isomers of $CH3CH=SO$ (methyl sulfine), were produced by pyrolyzing 2-methyl-2-propyl vinyl sulfoxide in a fumace maintained at $350\circ C$. A pulsed solenoid valve sampled the pyrolysis products in a Ne/He flow and the rotational spectra were obtained with a FT nucriwave soectrineter. Internal rotor splittings were observed for the ($Z$) form and a fit of the A-state normal isotopomer lines to a Watson Hamiltonian gave rotational constants of A = 14237.0861(5) MHz, B = 4678.4488(3) MHz and C = 3594.8008(2) MHz. A oartuak $r3$ structure of the ($Z$) isomer was determined from spectral assignments of a sulfur-34, two carbon-13 and two deuterium-substituted methyl group isotopomers. The spectral data show that one methyl dydrogen is located in the heavy atom plane oriented syn with respect to the oxygen. Electric dipole moment components of $\mu a$ = 2.714(5) D and $\mu b$ = 1.869(35) D were calculated from Stark shift measurements of the ($Z$) isomer. The ($E$) isomer did not exhibit internal rotor splittings and a fit of normal isotopomer $a$-type transitions to a Watson Hamiltonian gave A = 31128(27) MHz, B = 3475.8521(16) MHz and C = 3188.4429(23) MHz. An ($E$):($Z$) ratio of 3:97 is estimated from a comparison of line intensities of the normal isotopomer of the ($E$) form with line intensities of the sulfur-34 isotopomer of the ($Z$) isomer.