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>Direct IR laser absorption spectroscopy of jethyphen;cooled CO2HF complexes: Analysis of the ngr;1HF stretch and a surprisingly low frequency ngr;6intermolecular CO2bend
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Direct IR laser absorption spectroscopy of jethyphen;cooled CO2HF complexes: Analysis of the ngr;1HF stretch and a surprisingly low frequency ngr;6intermolecular CO2bend
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机译：Direct IR laser absorption spectroscopy of jethyphen;cooled CO2HF complexes: Analysis of the ngr;1HF stretch and a surprisingly low frequency ngr;6intermolecular CO2bend
High sensitivity, tunable laser direct absorption methods are exploited to obtain high resolution IR spectra (Dgr;ngr;lsim;0.001 cmminus;1) of weakly bound CO2HF complexes in a pulsed supersonic slit jet expansion. Transitions from the ground vibrational state corresponding to a single quantum excitation of the ngr;1HF stretch are observed and analyzed with a semirigid linear molecule Hamiltonian. The observed increase in bothB(+1.75percnt;) andD(+55percnt;) upon ngr;1excitation is inconsistent with the commonly used diatomic approximation, and is not possible to rationalize for a nearly linear upper state geometry with small amplitude zero point motion of the intermolecular CO2bend coordinate. We consider an alternative centrifugal straightening mechanism which predicts large centrifugal distortion effects due to end over end rotation of a complex with a nonlinear vibrationally averaged geometry in a weak bending potential. In support of this interpretation, hot band spectra are observed arising from bend excited complexes significantly populated in the 16 K expansion; intensity based estimates of the internal excitation indicate a surprisingly low bend frequency of 10plusmn;5 cmminus;1. A preliminary analysis of the spectra asldoubling in a Pgr;larr;Pgr; vibrational hot band for a linear equilibrium geometry is presented. An alternative interpretation of the spectrum as asymmetry doubling of aK=1larr;1 rotational hot band for a bent geometry is also considered. This latter interpretation is more consistent with the data and predicts a CO2bend angle in the complex forK=1 between 25deg; and 30deg;. Linewidths for the upper vibrational states in CO2HF exhibit homogeneous broadening 3ndash;4 times in excess of the apparatus resolution. Voigt analysis of the absorption line shapes indicates linewidths (FWHM) of 136plusmn;16 MHz and independent ofJstate; this corresponds to a relaxation lifetime of 1.1plusmn;0.2 ns for HF in the complex.
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