The infrared spectra of acetonitrile and acetonitrile-d3 have been studied at − 50°C for the high-temperature (β) crystalline phase and at − 65°, − 115° and − 192°C for the low-temperature (α) crystalline phase. A powder x-ray pattern obtained at liquid-nitrogen temperature indicates that the unit cell is primitive orthorhombic and that it contains eight molecules. It is shown that the consideration of all available structural data together with the site group and factor group splittings for the α crystal tends to favor D2h1 (Pmmm) and D2h9 (Pbam) as possible space groups.

We report the surface plasmon study on a variety of self-assembled monolayers (SAMs) of n-alkanethiols, HS(CH2) n CH3 (n = 11, 13, 15, 17, 19), absorbed to silver and gold surfaces, in terms of thicknesses, indices, and tilt-angles. We have found that the refractive indices for the alkanethiols attached to Ag increase gradually as alkyl chain length increases. Likewise, the refractive indices for Au increase gradually to an alkyl chain length of n = 17, at which point its refractive index decreases slightly. The indices vary from a low value of 1.33 to 1.44. This gradual increase in index is not unexpected since it suggests that differences in packing and consequent bulk polarizability, χ(1), is affected by alkyl chain length. A molecular modeling minimized n-alkanethiol length and its corresponding experimental surface plasmon thickness were used to determine the tilt-angle for each of the various alkanethiols via a projection analysis. We found that the tilt-angles of the n-alkanethiols attached to Ag begin to increase from 0° starting with n = 15; however, the tilts on Au have an average of ∼41°, seemingly independent of carbon chain length.

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The rates of reaction of singlet oxygen with 25 hydrazines were determined by following the emission of singlet oxygen at 1270 nm as a function of time. These data are utilized to discuss various options for the quenching mechanism including electron transfer, electronic to vibrational energy transfer, and a contact charge-transfer process.It is now well established that singlet oxygen is responsible for photodynamic destruction of both biologically and commercially important molecules. As a consequence, it is of some practical importance to search for and to investigate the properties of molecules capable of physically quenching1 this reactive species.Molecules that have been identified as physical quenchers of singlet oxygen include amines,2 ~ulfides,~ carotenoids: metal chelates,lb nitroxides,Ib phenols,lb inorganic anions,Ib and nitroso compounds.Ib It has been recognized that physical quenching of IO2 occurs by four distinctly different mechanisms:1a (an energy-transfer mechanism (for example, carotenoids have low-lying excited states ( I ) (a) Foote, C. 7 R , = R , = M e ; R 3 -R 4 -1 9 u 8. R, = R 2 = Me; R 3 = R 4 = necPe 9. R, .Rz. R,= Me; R , = iBu I O . R~-R , = R , = M~. R4-necPe 12. R, = R,. Me: R, = R, = necPe 11. R , = R 3 = M e . R,-R,=ISu 13. R, = R z = R , = R , = C & 2 2 2 3 2 4 2 5capable of accepting the energy from the IAg state of 02); (2) a reactive quenching mechanism that involves covalent bonding of IO2 to a substrate followed by decomposition to triplet oxygen 0002-7863/90/ 151 2-5080$02.50/0 Q

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