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WEI CHEN, JENS-UWE GRABOW, MICHAEL J. TRAVERS, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138; and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; STEWART E. NOVICK, MICHAELEEN R. MUNROW, Department of Chemistry, Wesleyan University, Middletown, CT 06459; M. C. MCCARTHY, P. THADDEUS, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138; and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.
The ground state rotational spectra of four methylcyanopolyynes, CH3(C \equivC) 2CN, CH3(C \equivC) 3CN, CH3(C \equivC) 4CN, and
CH3(C \equivC) 5CN, were measured between 6 and 22 GHz by Fourier transform microwave spectroscopy. For CH3(C \equivC) 2CN, 8 transitions, each with nitrogen nuclear quadrupole hyperfine structure (hfs), were observed and a value of eqQ = -- 4.25(3) MHz was determined for the first time. Twenty-one rotational transitions of CH3(C \equivC) 3CN, ten rotational transitions of CH3(C \equivC) 4CN, and eleven rotational transitions of CH3(C\equivC) 5CN were detected for the first time and precise values for the rotational, leading centrifugal distortion constants of each molecule, and the nuclear quadrupole coupling constant of CH3(C \equivC)3CN were determined.