Microwave Structure for the Propiolic Acid-Formic Acid Complex

作者：Kukolich Stephen G^*; Mitchell Erik G; Carey Spencer J; Sun Ming; Sargus Bryan A

来源：Journal of Physical Chemistry A, 2013, 117(39): 9525-9530.

DOI：10.1021/jp312201r

New microwave spectra were measured to obtain rotational constants and centrifugal distortion constants for the DCCCOOH center dot center dot center dot HOOCH and HCCCOOD center dot center dot center dot DOOCH isotopologues. Rotational transitions were measured in the FAST SWITCH frequency range of 4.9-15.4 GHz, providing accurate rotational constants, which, combined with previous rotational constants, allowed an improved structural fit for the propiolic acid-formic acid complex. The new structural fit yields reasonably accurate orientations for both the propiolic and formic acid monomers in the complex and more accurate structural parameters describing the hydrogen bonding. The structure is planar, with a positive inertial defect of Delta = 1.33 amu angstrom(2). The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations. The best-fit hydrogen bond lengths have an r(O1-H1 center dot center dot center dot O4) of 1.64 angstrom and an r(O3-H2 center dot center dot center dot O2) of 1.87 angstrom. The average of the two hydrogen bond lengths is r(av)(exp) = 1.76 angstrom, in good agreement with r(av)(theory):= 1.72 angstrom. The center of mass separation of the monomers is R-CM = 3.864 angstrom. Other structural parameters from the least-squares fit using the experimental rotational constants are compared with theoretical values. The spectra were obtained using two different pulsed beam Fourier transform microwave spectrometers.

• 出版日期2013-10-3