Microwave spectroscopy of the ν8- ν6 band of diacetylene

Abstract

Vibration-rotation transitions of diacetylene between the first excited states of the ν 6 (CCH symmetric bending) and the ν 8 (CCH antisymmetric bending) vibrations were observed with a Stark modulation microwave spectrometer. The rotational, centrifugal distortion and l-type doubling constants of the two vibrational states were determined as follows with 2.5 σ uncertainties in parentheses. B v ( MHz) D v ( kHz) q v ( MHz) ν 6 4391.3230(84) 0.582(154) 2.4830(32) ν 8 4391.1921(94) 0.594(179) 2.4073(37) The ν 8- ν 6 band origin was obtained to be 71 868.336(57) MHz [2.3972696(19) cm −1]. The transition dipole moment of the ν 8- ν 6 band was precisely determined from a measurement of the Stark effect to be 0.0787(10) D, which indicates that the change in dipole moment induced by a deformation of the CCH angle is appreciably larger in diacetylene than it is in acetylene.