Millimeter Wave Rotational Spectrum and Centrifugal Distortion

Intensive studies have been carried out on the rotational spectra of various isotopic species of ketene, H2C = C = 0 , since 1950 [ 1 6 ] . The centrifugal distortion analysis of ketene [3, 4 ] , together with information from additional infrared data [3, 5 ] , enabled Mallinson and Nemes [6] to reevaluate the molecular force field for ketene. Recently, microwave investigations on the higher homologues thioketene, H2C = C = S [7, 8] , and selenoketene, H2C = C = Se [9, 10] , have been reported. The first interstellar microwave detection of interstellar ketene was reported in 1977 by Turner [11] . The detection in the source Sgr B2 was based on three transitions: 514 — 413 , 515 — 414 and 413 — 312 at the frequencies 101981.39, 100 094.51 and 81 586.19 MHz, respectively. Further millimeter wave transitions were tentatively detected and assigned. Recently, Thaddeus and coworkers have identified isothiocyanic acid, HNCS [12], and methyl mercaptan, CH3SH [13] , in SgrB2 from observations of a number of millimeter wave