No abstract

An analysis has been made of the primary atomic and molecular products arising from O3 photodissociation at 1576 Å. The yield of oxygen atoms is 1.90±0.30, of which 71% are O(3P) and 29% are O(1D). Since a primary yield greater than unity can only be a consequence of three-fragment dissociation, these results suggest that fragmentation into three O(3P) atoms, and production of O(1D) plus a singlet oxygen molecule, have comparable yields. Observation of prompt emission in the 7300–8100 Å spectral region indicates that the singlet O2 is O2(b 1∑+g). Vibrational levels in the range v=0–6 have been detected, the distribution corresponding to a vibrational temperature of 104 K. This study is the first to show photodissociative production of the O2(b 1∑+g ) state in any system.

core of the high Rydberg state (RH+-e") may have an unpaired electron distribution similar to that of the radical cations, the C-H bond scission at the chain end is again expected. The observed selective formation of 1-alkyl radical from the crystalline neat linear alkane8 is thus quite reasonable from the view of the unpaired electron distribution in the linear alkane radical cations observed in SF6 and in other halocarbon matrices.1 23 It is well-known that only the fully extended chains exist in the crystal of linear alkanes.17 So, there may be no possibility of forming the primary cations with the gauche conformation in the neat crystals. The above-mentioned observations and their interpretation are strongly supported by the present work, which gives clear evidence for the correlation of the unpaired electron density and the site selection of deprotonation from the linear alkane radical cations with the extended conformations. Concluding RemarksThe present work clearly indicates that the linear alkane radical cations with the extended structure undergo selective deprotonation from the chain end, as is expected from the unpaired electron distribution when the extended conformer is exclusively formed (17) Kanesaka, I.; Synder, R. G.; Strauss, H. L. J. Chem. Phys. 1986, 84, 395 and references cited therein. and the population of the gauche conformer is negligible even at elevated temperature, at which the deprotonation reaction proceeds. Formation of the 2-alkyl radical is expected from the gauche conformer, in which the unpaired electron density is higher in the in-plane C-H bond at the C2 atom than that in the other end. The observation of the 2-alkyl radical formation in CF-C12CF2C1, in which the gauche conformer is often stabilized, may be ascribable to the higher rate of deprotonation from the gauche form because of the higher unpaired electron density in the in-plane C-H bond at C2 than that at C, in the corresponding extended conformer. This idea has been suggested in our earlier paper,2 in which we did not use the terminology of the gauche conformer but what is meant is the same. The citation of this description by Lund et al. as a structure in their discussion is a misunderstanding.10b'dThe present work not only gives strong support for our interpretation for the selective formation of the 1-alkyl radical in the radiolysis of neat crystalline linear alkanes8 but also may play a crucial role in clarifying the confusion resulting from arguments reported by Lund and his co-workers9•10 on the structure and reactions of the alkane radical cations.

Photodissociation of C2N2 at the 1576 Å F2 laser line generates CN(A 2Π) up to the thermodynamic limit of v=5, with a bimodal vibrational distribution peaking at v=0 and v=2. Radiative lifetimes for the six observed levels have been obtained by extrapolating time decays to zero pressure, and the data show rapidly decreasing lifetimes with increasing v, in accord with recent theoretical predictions, and contrary to previous experimental determinations. The range of lifetimes observed is 4.3–8.5 μs. Quenching of these levels by the parent molecule shows a factor of 12 increase in rate coefficient in going from v=0 to v=5, correlated to the energy gap between the A 2Π state and the closest lower X 2Σ+ level, suggesting that the quenching mechanism is one involving cross relaxation between CN(A) and CN(X).