New high-resolution analysis of the ν7 and ν9 fundamental bands of trans-formic acid by IR Fourier transform and millimeterwave spectroscopies

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Absolute line intensities for formic acid and dissociation constant of the dimer

Absolute line intensities in the v6 and v8 interacting bands of trans-HCOOH, observed near 1105.4 and 1033.5 cm -1, respectively, and the dissociation constant of the formic acid dimer (HCOOH)2 have been measured using Fourier transform spectroscopy at a resolution of 0.002 cm-1. Eleven spectra of formic acid, at 296.0(5) K and pressures ranging from 14.28(25) to 314.0(24) Pa, have been recorded between 600 and 1900 cm-1 with an absorption path length of 19.7(2) cm. 437 integrated absorption coefficients have been measured for 72 lines in the v6 band. Analysis of the pressure dependence yielded the dissociation constant of the formic acid dimer, k p=361(45) Pa, and the absolute intensity of the 72 lines of HCOOH. The accuracy of these results was carefully estimated. The absolute intensities of four lines of the weak v8 band were also measured. Using an appropriate theory, the integrated intensity of the v6 and v 8 bands was determined to be 3.47 × 1017 and 4.68 × 10-19 cm-1/(molecule cm-1) respectively, at 296 K. Both the dissociation constant and integrated intensities were compared to earlier measurements. © 2007 American Institute of Physics.