Two-step laser optogalvanic spectroscopy of the odd-parity Rydberg states of atomic mercury

We present new experimental data on the highly excited levels in mercury using the two-step laser excitation and optogalvanic detection technique in conjunction with a RF discharge cell. The 6s7s S-3(1) intermediate level has been accessed from the 6s6p P-3(2) metastable level that is collisionally populated in the mercury discharge in the presence of a buffer gas at a pressure of about 1 Torr. Two beams from two different dye lasers pumped with a common excimer laser were passed through the discharge cell containing mercury vapors. The first laser was tuned to 6s7s S-3(1) level whereas the second laser was scanned covering the wavelength region between 544-458 nm. We have observed the 6snp P-3(0) (10less than or equal tonless than or equal to18), 6snp P-3(1) (10less than or equal tonless than or equal to41), 6snp P-3(2) (10less than or equal tonless than or equal to70) and 6snp P-1(1) (10less than or equal tonless than or equal to42) Rydberg series. The 6snp P-3(2) Rydberg series to such high n-value has been reported for the first time. The first ionization potential of mercury is determined from the 6snp P-3(2) Rydberg series as 84184.15+/-0.05 cm(-1). Some collisionally induced parity forbidden transitions have also been located that are identified as 6sns S-1(0) (40less than or equal tonless than or equal to58) series.