The infrared spectrum of isoxazole in the range 600-1400 cm(-1), including a high-resolution study of the v(7)(A ') band at 1370.9cm(-1) and the v(16)(A '') band at 764.9cm(-1), together with ab initio studies of the full spectrum

• The high resolution infrared gas phase spectrum of isoxazole in the range 600-1400 cm(-1) has been recorded and more precise centres obtained for a number of bands; analyses of the nu(7)(A') band at 1370.9 cm(-1) and the nu(16)(A") band at 764.9 cm(-1) have been performed. Use of the Watson Hamiltonian, A-reduction, IIIr-representation and simultaneous analysis of the present IR and previous microwave data, has led to rotation constants and quartic centrifugal distortion constants Delta(J), Delta(JK), Delta(K), delta(J) and delta(K) for the ground state and for the nu(16) vibrationally excited states. The equilibrium structures and the derived harmonic frequencies have been calculated by ab initio methods using triple zeta + polarization (TZVP) and cc-pVTZ basis sets, with MP2, MP4 and CCSD(T) methods. At each methodology, for closest numerical agreement between the calculated and observed rotation constants, the optimum basis set seems to be TZVP rather than cc-pVTZ basis sets. However, the order of the highest A" and lowest A' symmetry vibrations is only resolved by the cc-pVTZ basis set with the MP4 methodology, which does generate the experimental sequence (nu(14)>nu(13)). The CCSD(T) methodology does not lead to significant difference over either MP2 or MP4 with the TZVP basis set.

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NATURVETENSKAP  -- Fysik -- Atom- och molekylfysik och optik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Atom and Molecular Physics and Optics (hsv//eng)

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