A laser spectroscopic investigation of rhodium monosilicide

Laser-induced fluorescence experiments, using Rh metal and silane and jet-cooling, reveal a rich band spectrum of RhSi in the UV-visible region between 420 and 520 nm.This represents the first such observation for this free radical. The molecular ground state is identified as a 2Σ+ state derived principally from a σ2π4δ4σ1 configuration and the electronic transition arises from promotion of the unpaired σ electron, localized on the Rh atom, to a ligand-sensitive π-orbital which is anti-bonding. A (0,0) band of the [22.6] 2Σ+-X2Σ+ system has been recorded near 442.55 nm at 200 MHz resolution. The band is red-degraded and all the rotational structure is resolved and a small hyperfine splitting has been measured. The (0,0) sub-bands of the [20.2]2Π-X2Σ+ system lie near 495 nm. All bands of the system are strongly red-degraded. The (2,0) sub-bands have been recorded at 200 MHz resolution; all the rotational structure is resolved and a small hyperfine splitting measured, however, the upper states have proven to be perturbed. Dispersed fluorescence from numerous bands has been examined. Analysis of all the data provides the following molecular parameters for the X2Σ+ state (in cm−1): B0 = 0. 183695, D0 = 3.76 × 10−8, γ0 = −0.05083, γ0D = 1.08 × 10−5, and ωe = 522. The measured bond length is 0.2043 nm. A simple molecular orbital scheme accounts for the observations.