15min:
DETECTION AND ANALYSIS OF ROTATIONALLY RESOLVED TORSIONAL SPLITTINGS IN PHENOL (C6H5OH): THE HIGH RESOLUTION FTIR SPECTRUM OF PHENOL BETWEEN 600 AND 1300 CM-1.

SIEGHARD ALBERT, MARTIN QUACK, PHYSICAL CHEMISTRY, ETH ZÜRICH, CH-8093 ZÜRICH, SWITZERLAND.

One of the great challenges of high resolution infrared spectroscopy is to understand the rovibrationally resolved spectra and dynamics of large molecules involving numerous degrees of freedom and large amplitude motions like bending, torsion or inversion modes\footnoteS. Albert and M. Quack, ChemPhysChem \textbf2007, 8 , 1271, M. Quack, J. Mol. Struct. \textbf1995, 347 , 245.. Complicated resonance networks can be built up through the coupling of such modes and the energy flow can be studied upon excitation\footnoteH. R. Dübal and M. Quack, J. Chem. Phys. \textbf1984, 81(9) , 3779. M. Quack, Ann. Rev. Phys. Chem. \textbf1990, 41 , 839.\footnoteS. Albert, M. Winnewisser and B.P. Winnewisser, Ber. Bunsenges. Phys. Chem. \textbf1996, 100 , 1876, S. Albert, M. Winnewisser and B.P. Winnewisser, Ber. Bunsenges. Phys. Chem. \textbf1997, 101 , 1165.. Excellent examples of the study of such phenomena are the FTIR spectra of aromatic systems which can now be rovibrationally resolved using state-of-the-art technology\footnoteS. Albert, K.K. Albert and M. Quack, Trends in Optics and Photonics \textbf2003, 84 , 177.. As a benchmark molecule we shall discuss phenol. Its vibrational spectrum has already been assigned at low resolution\footnoteH.D. Bist, J. Brand and D.R. Willams, J. Mol. Spectrosc. \textbf1967, 24 , 402. and its photodissociation has been studied recently\footnoteM.L. Hause, Y.H. Yoon, A.S. Case and F. Crim, J.~Chem.~Phys. \textbf2008, 128 , 104307.. Its rotationally resolved infrared spectrum has now been recorded in the range 600--1300~cm-1 with our Bruker ZP2001 spectrometer with a resolution of better than 0.001~cm-1. This spectrum was used in an analysis of the out-of-plane modes nu4 ( nu0 = 687.00544~cm-1) and nu17b ( nu0 = 881.70033~cm-1). Here, no torsional splittings or resonances were observed, as opposed to the spectrum of the a-type bands nu12 (OH-sensitive), 2 nu18b (OH-sensitive), nu7a (CO-stretch), beta (OH-bend) and the combination bend nu17b + tau (CH-bend + torsion). We will discuss the J-dependent doublets with splittings ranging from 0.01 to 0.04~cm-1 observed in the rovibrational spectra, and will present an analysis of the combination band nu17b + tau with band centers of the two torsional components nu0a = 1198.24163~cm-1 and nu0b = 1198.20114~cm-1. A comparison between the phenol and fluorobenzene spectra will also be presented.