Byeong-Seo Cheong

Enhanced Raman spectrum of lawsone on Ag surface: Vibrational analyses, frequency shifts, and molecular geometry

The surface-enhanced Raman spectrum of lawsone, a well known natural dye, has been investigated. Activation with KNO(3) or Na(2)SO(4) solution was necessary to enhance the Raman signal, whereas addition of NaCl solution depletes the effects. In the enhanced Raman spectrum, the strong double-bond stretching bands are most distinctive and show large red shifts from those in the infrared and FT-Raman spectra. The observed strong double-bond stretching bands reflect lawsone coordinated perpendicular to the Ag surface. DFT computations have been carried out for the plausible configurations of lawsone coordinated to an adatom on the Ag surface. Lawsone coordinated to an Ag(+) adatom with H(+) released best reproduces the observed vibrational characteristics.

Solvation of LiClO4 and NaClO4 in deuterated acetonitrile studied by means of infrared and Raman spectroscopy

Vibrational characteristics of CD3CN solutions of LiClO4 and NaClO4 have been studied by means of infrared and Raman spectroscopy. Blue shifts of 22 and 11 cm(-1) of the v2 C[triple bond]N stretch are observed resulting from interaction of CD3CN with Li+ and Na+, respectively. The number of primary solvation sites of both Li+ and Na+ in acetonitrile is believed to be four from the comparison of the Raman intensities of the C[triple bond]N stretch for free CD3CN and those coordinated to Li+ and Na+. Evidently formation of contact ion pairs of the cation (Li+ or Na+) and anion (ClO4-) is more probable at a higher concentration of the salt. The characteristics of the v2 C[triple bond]N stretch, v4 C-C stretch, and v8 CCN deformation bands vary substantially upon coordination, while other vibrational bands are relatively immune to the donor-acceptor interaction. DFT calculations have also been performed at the BLYP/6-31 + G(2d,p) level to examine the structures and vibrational characteristics of CD3CN coordinated to Li+ and Na+. The calculated results are in good agreement with the observed vibrational characteristics.

A theoretical investigation of the structure and vibrational properties of the methyl isocyanide dimer

Abstract Ab initio calculations have been carried out to study the geometrical and vibrational properties of the methyl isocyanide dimer. Calculations show that there is a stable dimer structure of C 2h symmetry, consistent with previous results. Rotation of a methyl group by 60° from the minimum-energy configuration leads to a transition state of C s symmetry, whereas rotation of both methyl groups by 60° from the minimum-energy configuration leads to a second-order saddle point of C 2h symmetry. The geometry of methyl isocyanide is only slightly affected by dimerization, and the dimer turns out to be principally a N C dipole pair. Change of the vibrational characteristics upon dimerization is relatively small and well reproduced theoretically. The distinct hypysochromatic shift of the N C stretch in complexation is small, but clearly observed in dimerization of methyl isocyanide. Strengthening of the N C bond in dimerization is further confirmed with the higher N C force constant of the dimer.