High resolution FTIR spectroscopic study of the ν4 band of CH3CHF2 enclosed in a flow of cold N2 gas

An enclosive flow cooling (EFC) cell has been constructed, and coupled to a Bruker IFS 120HR high resolution Fourier transform spectrometer to record rotationally cold absorption spectra of gases of atmospheric interest at high spectral resolution. The new system has been characterized using NO, revealing that rotational temperatures as cold as 110 K are readily attainable using liquid nitrogen as a cryogen. Infrared spectra of the v(4) band of 1,1-difluoroethane (R152a), CH3CHF2, cooled in the EFC cell have been measured at a resolution of 0.0019 cm(-1). Eight hundred and twenty rovibrational transitions of the weak 1,4 band with 2 less than or equal to J' less than or equal to 46 and K-c' less than or equal to 16 were assigned and fitted to Watson's A-reduced Hamiltonian. The v(4) CH3 symmetric deformation (a/c-type) was found to be coupled to the v(13) asymmetric deformation (h-type) via an a-axis Coriolis interaction. In the ensuing analysis, values of spectroscopic constants were obtained for both the v(4) and dark v(13) states. Supporting ab initio calculations up to the MP2/ TZV+(3df,3p) level are presented. (C) 2002 Elsevier Science (USA). All rights reserved.