FTIR SPECTROSCOPY OF THE $\nu_4$ BANDS OF $^{14}$NO$_3$ and $^{15}$NO$_3$

Abstract

High-resolution Fourier transform infrared spectra of the NO$_3$ $\nu_4$ bands of $^{14}$N and $^{15}$N isotopic species were observed in the 365 and 360 cm$^{-1}$ region. Observed lines were used to determine $\Delta$K=3 combination differences of the ground state coupled with transition frequencies of the $\nu_3$ hot band $\nu_3$ + $\nu_4$ - $\nu_4$ in 1127 cm$^{-1}$ region \textbf{268}, 85 (2011).} and $\nu_3$ + $\nu_4$ band in 1492 cm$^{-1}$ region, which made it possible to determine the rotational C$_0$ constants of 0.228 6321(67) cm$^{-1}$ and 0.228 674(11) cm$^{-1}$ for $^{14}$NO$_3$ and $^{15}$NO$_3$ , respectively. Inertial defects of several vibrational states were calculated by using a formula of Jagod and Oka \textbf{139}, 313 (1990).} and compared with the observed values. Although the observed Coriolis coupling constants $\zeta$$_4$=-0.188 ($^{14}$NO$_3$ ) and -0.156 ($^{15}$NO$_3$ ) are largely different from the expected value of -0.7 from a force field calculation, observed inertial detects are in good agreement with calculated values, for example, $\Delta_{obs}$(Gr.)= 0.206 [0.223] amu\AA$^2$, (v$_4$=1) 0.434[0.437] amu\AA$^2$ etc, where calculated values are given in square brackets.