The C-H Bending Fundamental Band Of Formic Acid Dimer

Hydrogen bonds play an important role in physics,chemistry and biology.Formic acid dimer(FAD)is a prototype for studying intermolecular hydrogen bond and multiple proton transfer dynamics.Because the two protons in the intermolecular hydrogen bonds of FAD can transfer concertedly between the two formic acid subunit,each rotation-vibrational energy level will be split into two tunneling components.Determining the tunneling splitting in FAD experimentally can test various quantum chemical models and computational methods.The rotationally-resolved infrared spectrum the C-H bending fundamental band of(HCOOH)2 has been measured by using a segmented rapid-scan distributed-feedback quantum cascade laser absorption spectrometer to probe a slit supersonic jet expansion.In the spectral region of 1367.041-1377.5 cm-1,a total of 1143 transition with J up to 32 and Ka up to 16 were assigned to the C-H bending fundamental band of(HCOOH)2.Strong local perturbations caused by the rotation-tunneling coupling between two tunneling components were observed in(HCOOH)2.With the help of PGOPHER program,the C-H bending fundamental band and the previously recorded C-O stretching fundamental band of(HCOOH)2 were analyzed together,yielding precise rotational constants,centrifugal distortion constants,and vibration-rotation coupling constants,etc.The band-origin of the C-H bending fundamental band of(HCOOH)2 is 1371.77696(11)cm-1.The tunneling splitting in the ground state and the C-H bending excited state is 0.01198(11)cm-1 and 0.00105(22)cm-1,respectively.