GOU QIAN, GANG FENG, LUCA EVANGELISTI AND W. CAMINATI, Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, I-40126 Bologna, Italy; MONTSERRAT VALLEJO LÓPEZ, ALBERTO LESARRI, Departamento de Quimica Fisica y Quimica Inorganica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain; EMILIO COCINERO, Departamento de Quimica Fisica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco, E-48080 Bilbao, Spain.

The rotational spectra of three 1:1 complexes of formaldehyde (H2CO) with freons, i.e. difluoromethane (CH2F2), fluorochloromethane (CH2FCl) and trifluorochloromethane (CF3Cl), have been observed and assigned using pulsed jet Fourier transform microwave technique. Several isotopologues (including some 13C species) have been measured in natural abundance. The tunnelling splittings have been measured in the first two adducts with relative intensity 1:3, due to the internal rotation of the formaldehyde moity along its symmetry axis. The barriers to this motion have been estimated by using a flexible model. For the latter two complexes, each of transition displays the hyperfine structures due to the quadrupolar effects of 35Cl (37Cl) nucleus. The dissociation energy has been estimated within the pseudo-diatomic approximation for all three complexes.