Ct. Kingston et al., Anomalous vibrational dependence of the rotational and hyperfine parameters in the B-4 Pi-X-4 Sigma(-) transition of NbO, J MOL SPECT, 207(1), 2001, pp. 104-112
The laser excitation spectrum of jet-cooled NbO in the region 16 000-18 000
cm(-1) has been recorded at high resolution, giving rotational and hyperfi
ne constants for the levels v = 0-3 of the B(4)Pi state and v = 1 of the X(
4)Sigma (-) state; zero gaps have also been measured at low resolution for
some weaker bands involving higher vibrational levels. Taken together with
the laser data for the B-X (0,0) band from Adam et al. (J. Chem. Phys. 94,
6240-6262 (1994)) and the Fourier transform emission data for the doublet m
anifold from Launila et al. (J. Mol. Spectrosc. 186, 131-143 (1997)), the n
ew data give a very complete picture of the vibrational energy level patter
n in this region. Strong irregularities in the vibrational dependences of t
he B(4)Pi rotational and hyperfine constants can be interpreted in terms of
spin-orbit interaction between the B(4)Pi state and the f(2)Pi, c(2)phi, a
nd d(2)Delta states. The interaction is strong enough that all three double
t states can be seen in absorption from the X(4)Sigma (-) ground state, add
ing to the complexity of the spectrum. The hitherto unknown sigma delta sig
ma* (4)Delta state is estimated to lie near 17 500 cm(-1), from the change
of sign in the spin-rotation parameter gamma of the B(4)Pi state between v
= 2 and 3. (C) 2001 Academic Press.