Absorption coefficient unsaturated

As expected, the incorporation of pendant unsaturation in the resists greatly enhances sensitivity as demonstrated by a comparison of the contrast curves for poly(N-aiiyl maleimide-VBC) and the structurally similar poiy(N-ethyl maleimide-VBC) (Figure 4). Both polymers have similar molecular weights and nearly identical mass absorption coefficients but the allyl-containing copolymer is 5X faster. 

This weak transition is due to the promotion of an electron from the non-bonding molecular orbital n to an anti-bonding tt orbital. This transition is usually observed in molecules that contain a heteroatom as part of an unsaturated system. The most common of these bands corresponds to the carbonyl band at around 270 to 295 nm, which can be easily observed. The molar absorption coefficient for this band is weak. The nature of the solvent influences the position of absorption bands because the polarity of the bond is modified during absorption. For example, ethanal Amax = 293 nm (e = 12 in ethanol as solvent). 

Lewis acid (BF3 or EtAlC ) complexes of a,(3-unsaturated esters can shift the photoequilibrium (PSS) toward the thermodynamically less stable Z-isomer even more and may inhibit other competing unimolecular photochemical processes.563 Such enhanced isomerization results are explained by selective excitation of the ground-state Lewis acid ester carbonyl complex, which exhibits a red shift in the long-wavelength k,k absorption band (/lmax) and higher molar absorption coefficients ( 313) (Scheme 6.6). 

D 3030 VOLATILE MATTER OF VINYL CHLORIDE RESINS D 3045 HEAT AGING OF PLASTICS WITHOUT LOAD D 3124 VINYLIDENE UNSATURATION NUMBER BY FTIR D 3291 COMPATIBILITY OF PLASTICIZERS/COMPRESSION D 3349 ABSORPTION COEFFICIENT/PE CARBON BLACK D 3351 GEL COUNT OF PLASTIC FILMS... 

Because of this population depletion the absorption coefficient a(o)) = decreases from its unsaturated value aQ(u))... 

Putting the relations (10.41-45) together, we can express the difference - a at the line center wq by the unsaturated absorption coefficient 0 " saturation parameter Sq(o)q), and a numerical factor Cjj ... 

A considerable difference has been observed between the spectrum of cyclohexyl and that of the cyclopentyl radical, the former exhibiting a pronounced shoulder at 250 nm with e = 920 m -1 cm-1. Cyclohexenyl and cyclopentenyl radicals show a much stronger absorption with definite maxima at 240 nm. These are allyl type radicals and like the allyl radical itself they show extinction coefficients of 7000-9000 M -1 cm-1. The optical spectrum of the allyl radical is greatly affected by unsaturated substituents which conjugate with the allylic 1 and 3 positions. These positions bear all the spin density and their interaction with carboxyl groups, for example, shifts max to 270 nm with extinction coefficients of 20,000-40,000 M 1 cm 1 (Neta and Schuler, 1975). A carboxyl group attached to the central carbon of allyl has only a minimal effect on the absorption. 

---