Knowledge Bank

The high-resolution infrared spectra of jet-cooled methoxy radical $(CH3O)$ in the region $2850-2940cm-1$ have been recorded in pulsed slit jet expansions with the excimer laser flash photolysis method. A perpendicular band centered at $2885.7cm-1$ was assigned to a portion of the C-H asymmetric stretch vibration of $CH3O$ using ground state combination differences. Five sub-bands with $P\prime \prime =-3/2,-1/2,+1/2,+3/2,+5/2$ and $J\prime \prime$ up to 8.5 have been assigned. The series of Q branches almost equally separated by $12.4cm-1$ with intensity patterns characteristic of perpendicular transitions supports the assignment. Because of the low jet temperature, the assigned transitions all arise from the $E3/2$ fine structure component of the ground state. The asymmetric C-H stretch vibration is subject to a strong Jahn-Teller effect, which should produce several subbands. The firm vibrational assignment of this band requires data for all C-H stretch bands. Least squares fitting of this band and scanning over more of the C-H stretching region scan for other bands are proceeding in our lab.