HF inversion in the 2,5-dihydrofuran center dot center dot center dot HF complex

The rotational spectrum of the hydrogen bond heterodimer 2,5-dihydrofuran . . . HF has been investigated in the frequency region 6-18.5 GHz using mole cular beam Fourier transform microwave spectroscopy. The R-branch mu (a)-ty pe spectra of the parent, 2,5-dihydrofuran . . . DF, C-13(alpha)-2,5-dihydr ofuran . . . HF and C-13(beta)-2,5-dihydrofuran . . . HF species have been measured. All the observed lines are split into two components due to the t unneling of HF between the two equivalent hydrogen bonding sites at the oxy gen atom. A value for the barrier to HF inversion of 100 cm(-1) has been ca lculated from the analysis of the rotational constants of both tunneling st ates on the basis of a simple one-dimensional model. Ab initio calculations at the MP2/6-311+G(d,p) and MP2/6-311+G(2df,p) levels of theory have been carried out to complement the experimental data. The results on the HF inve rsion barrier and hydrogen bond angular geometry of 2,5-dihydrofuran . . . HF have been compared to those previously obtained for the H2O . . . HF com plex. (C) 2001 American Institute of Physics.