Vibration-rotation-tunneling spectrum of formic acid dimer in the 7.3μm region

Abstract

The vibration-rotation-tunneling spectrum of formic acid dimer, (HCOOH)$_{2}$, in the spectral region 1369-1375 \wn has been measured by a multi-step rapid-can method in a slit jet expansion using a distributed-feedback quantum cascade laser. The observed spectrum is assigned to the O-C-H bending fundamental band. The tunneling splitting in the vibrational excited state is determined to be about 0.005 \wn, which is much smaller than that in the ground state, 0.0165 \wn (Goroya et al.,J. Chem. Phys. 140, 164311 (2014)). Strong local perturbations involving transitions with J > 9, K = 0 and 1 are identified in the observed spectrum. The deperturbation analysis will be presented.