Emission Spectroscopy and Ab Initio Calculations on IrN.

The emission spectrum of IrN was recorded in the near infrared using a Fourier transform spectrometer. The IrN molecules were excited in an Ir hollow cathode lamp operated with a mixture of Ne and a trace of N(2). Numerous IrN bands observed in the 7500-9200 cm(-1) region were assigned to a new a(3)Pi-X(1)Sigma(+) electronic transition with the 0-0 bands of the a(3)Pi(0)-X(1)Sigma(+) and a(3)Pi(1)-X(1)Sigma(+) subbands near 9175 and 8841 cm(-1), respectively. A rotational analysis of several bands of the 0-0 and 0-1 sequences was obtained and molecular constants were extracted. The effective Hund's case (a) constants for the new a(3)Pi state are: T(00) = 8840.31747(88) cm(-1), A(0) = -340.53329(93) cm(-1), DeltaG(1/2) = 984.3629(23) cm(-1), B(e) = 0.4699116(27) cm(-1), alpha(e) = 0.0030058(50) cm(-1), and r(e)= 1.6576432(47) Å. The spectroscopic properties of the ground state and several low-lying electronic states of IrN were also predicted by ab initio calculations. These calculations are consistent with our assignment of the a(3)Pi-X(1)Sigma(+) transition and also support our previous assignments of the A' (1)Pi and A(1)Pi electronic states [R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 193, 363 (1999)]. The excited a(3)Pi state of IrN has an 1varsigma(2)2varsigma(2)1pi(4)3varsigma(1)1delta(4)2pi(1) electron configuration and the configurations of the other low-lying electronic states are also discussed. Copyright 1999 Academic Press.