Quenching and enhancement of aroyl luminescence in excited nitrogen

This study investigates both decreases and increases of aromatic carbonyl p hosphorcescence in excited nitrogen, i.e., in a gas-chromatographic device called the aroyl luminescence detector (ALD), The ALD responds, with nigh s pecificity, to subpicogram amounts of strongly phosphorescing aroyls. Aroyl response may, however, be quenched by coeluting peaks or gaseous impuritie s. This deleterious effect has been investigated with O-2, H-2, CH4, and C3 H8 as model quenchers. Aroyl phosphorescence is more severely quenched than the nitrogen background, i.e,, the so-called second-positive system, N-2 ( C (3)Pi(u)) --> N-2 (B (3)Pi(g)), Oxygen, while being the strongest among t he tested quenchers of aroyl phosphorescence, is the weakest quencher of ni trogen emission; The efficiency of various quenchers is similar for aroyl c ompounds of similar structure. It differs, however-though not by more than a factor of 2-among aroyls of different chemical types. In contrast to thes e intensity-reducing effects, aroyl phosphorescence is significantly enhanc ed by the addition of argon to (the carrier and excitation gas) nitrogen. I t is proposed that the reaction sequence Ar*(P-3(0,2)) + N-2 --> N-2(C)* -- > N-2(B)* + hv --> N-2(A)* + hv results in an increased yield of the metast able N-2(A (3)Sigma(u)(+)) state (this state being considered responsible f or the n --> pi* excitation of aroyl compounds via an efficient triplet-tri plet: energy-transfer process).