The A(2Πi)–X(2Σ+) transition of the SiN radical by infrared diode laser spectroscopy

The A(2Πi)–X(2Σ+) 1,0 band of SiN has been observed in the 5 μm region by diode laser spectroscopy in a silane/nitrogen electrical discharge plasma. A detailed analysis of about 170 observed lines has led to a v=1 term value for the A state of 1972.443 73(24) cm−1 with 2.5 standard deviations in parentheses, which, when combined with optical data, was converted to the equilibrium term value of 993.9(2) cm−1. The analysis has clearly confirmed that the spin-orbit coupling constant in the A state is negative. The Λ-type doubling constants p and q in the A state have been determined for the first time, and other parameters including the rotational and spin-orbit coupling constants have been improved in accuracy by a factor of 100.