MOLECULAR-BEAM OPTOTHERMAL SPECTROSCOPY OF THE 9.6-MU-M NU-14-BAND OF BENZENE

The ν14 ℓ1u fundamental band of C6H6 has been recorded with sub-Doppler resolution under collisionless low-temperature molecular-beam conditions using bolometric detection of molecules excited by tunable microwave sidebands of a Lamb-dip-stabilized CO2 laser. The sidebands cover about 40% of the spectrum between laser lines in which 117 transitions for J, K ≤ 11 have been observed and fit to a precision of ±24 kHz, yielding improved ground and excited state rotational constants with nearly microwave accuracy. Our measured ground state rotational constant, B0 = 0.189 773 89 (3) cm-1, is compared with several disparate values reported previously. © 1991.