The rotational spectrum, structure, and molecular properties of the ethylenendash;HCl dimer

摘要

Three isotopic species of a hydrogen bonded dimer formed between ethylene and HCl have been observed through assignment of their rotational spectra using a pulsed, Fourier transform microwave spectrometer in which a gas mixture is pulsed into an evacuated Fabryndash;Perot cavity. The spectra unambiguously reveal a nonplanar, near prolate, asymmetric top (kgr; = minus;0.9880) in its ground vibrational state. The equilibrium structure hasC2Vsymmetry with the HCl on theC2symmetry axis of the dimer, perpendicular to the carbonndash;carbon bonding axis with the hydrogen atom located between the chlorine and the ethylene molecule, pointing midway between the carbon atoms. The chlorine atom is situated, on average, 3.724 Aring; from the edge of the ethylene molecule. The following spectroscopic constants have been obtained for the ethylenendash;H35Cl dimer: the rotational constants areA= 25 457(349),B= 2308.143(3), andC= 2167.970(3) in units of MHz; the chlorine nucleus quadrupole coupling constants are khgr;aa= minus;54.076(4), khgr;bb= 27.091(6), and khgr;cc= 26.985(10) in units of MHz, and the centrifugal distortion constants areDJ= 7.2(2) andDJK= 282(5) in units of kHz.