THE X2 2-PI-3/2-]X1 2-PI-1/2 ELECTRONIC BAND SYSTEMS OF LEAD MONOHALIDES IN THE NEAR-INFRARED

Emission spectra of the transitions X2 2-PI-3/2 --> X1 2-PI-1/2 of PbF, PbCl, PbBr and PbI have been observed in the near infrared spectral region. The X2 states of the radicals were excited by chemiluminescent reactions of lead atoms with molecular halogens and by E-E energy exchange from metastable NF(a 1-DELTA) or O2(a 1-DELTA(g)) molecules. For each molecule some sequences of blue-degraded bands were measured at spectral resolutions between 0.05 and 0.5 cm-1 using a Fourier-transform spectrometer. Analysis of the spectra yielded the ground state splittings of PbBr and PbI. The following electronic term values and vibrational constants of the X2 2-PI-3/2 states were obtained (in cm-1): T(e) = 8262.11(9), 8272.78(54), 8197.92(24), 7969.15(15), omega(e) = 533.12(15), 322.52(69), 218.35(45), 169.28(12), omega(e)chi(e) = 2.200(48), 0.878(219), 0.433(135), 0.323(24), for PbF, (PbCl)-Cl-35, (PbBr)-Br-79 and PbI, respectively, where the error limits are 3-sigma. Two complex bands near 7895 and 7390 cm-1 are tentatively assigned to HPbO (or PbOH) radicals.