| TECHNOLOGY |
Author has used electron diffraction to show that a pyridine molecule excited into a special state sheds its excess energy by opening up its ring - something never before predicted Ordinary electron diffraction techniques give distances between nuclei, revealing the structure of the compd. But author's group has developed a methodology with an instrument - whose construction was funded by NSF - that repeatedly takes electron diffraction "snapshots" of a reacting system every fraction of a PICOSECOND. Its success in producing such a detailed chemical movie has exceeded author's expectations. "It's so clean & neat - usually experiments don't cooperate like this" In particular, radiationless transitions are extraordinarily difficult to study because of their short timescales - on the order of a picosecond. The ultrafast electron diffraction technique is well suited to study this type of decay For 30 years, scientists have known that when some aromatic molecules in their excited singlet states are given enough vibrational energy, their usual form of decay - fluorescence - decreases while radiationless decay takes over. The phenomen, known as the CHANNEL-THREE PROCESS has been something of a mystery Chemists have proposed a number of possible ways that the molecule could return to a lower energy state - by twisting itself into different isomers. Author's group decided to examine the process by exciting pyridine above its channel-three-state threshold & watching it decay. To the researchers' surprise, all the intermediate structures previously proposed for the transition, such as the Dewar & Hueckel isomers, weren't forming. Instead, the researchers saw an extremely large internuclear distance between the pyridine's N & an adjacent C, indicating that the C-N bond had broken & ring had spread open |
| UPDATE | 12.01 |
| AUTHOR | This data is not available for free |
| LITERATURE REF. | This data is not available for free |
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