Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths. IX. The Spectra of the HCN and DCN Molecules from 2.5μ to 0.5μ

Abstract

The photographic infrared spectrum of HCN has been investigated using a 6‐meter concave grating spectrograph and absorption paths up to 600 meters. The near infrared spectra of HCN and DCN have been investigated using a grating infrared spectrometer with a lead sulfide cell as a detector. The interference fringes from a Fabry‐Perot etalon have been used as wavelength standards for the recording spectrometer. Twenty‐four bands of HCN and six bands of DCN have been measured. From these measurements earlier work has been corrected, and the zero‐order frequencies and anharmonic constants have been determined for both HCN and DCN. Perturbations have been found in the vibrational levels of HCN. Corresponding perturbations occur in the B_v values, and it has been shown that even apparently unperturbed B_v values are not linear functions of the vibrational quantum numbers. The B_e values for HCN and DCN were found to be 1.4849 cm⁻¹ and 1.2118 cm⁻¹. From these B_e values the C–H and C–N internuclear distances in the equilibrium position have been found to be 1.0657A and 1.1530A, respectively. From the zero‐order frequencies the force constants have been determined.