PNNL

Abstract

The rotationally resolved spectrum of a fundamental band of hydrogen fluoride tetramer has been recorded using a pulsed, slit jet diode laser spectrometer. The band has a parallel rotational structure and is assigned as the H-F out-of-plane libration fundamental with Au symmetry. Ninety-five ground state combination differences were fit to a symmetric top Hamiltonian to give the following ground state rotational constants: B" = 0.132081(7) cm-1, DJ" = 7.1(7) X 10-7 cm-1, DJK" = -9(2) X 10-7 cm-1, HJJJ" = 6(2) X 10-10 cm-1, HJJK" = 9(7) X 10-10 cm-1, HJKK" = -1.3(8) X 10-10 cm-1. A total of 190 transitions were fit to determine the upper state spectroscopic constants: v4 = 714.7849(1) cm-1, B' = 0.129634(5) cm-1, [delta](C ? B) = 0.001344 cm-1, DJ' = 6.4(5) X 10-7 cm-1, DJK' = -4.5(6) X 10-7 cm-1, [delta]DK = 2.92(8) X 10-6 cm-1, HJJJ' = 3(1) X 10-10 cm-1, HJJK' = 9(7) X 10-10 cm-1, HJKK' = -1.55(6) X 10-8 cm-1, [delta]HKKK'= -4.65(6) X 10-8 cm-1. Furthermore, a perpendicular band of Eu symmetry centered at 752.7 cm-1 has been assigned as the H-F in-plane libration fundamental of the HF tetramer. Finally a parallel band has also been observed at 741.0 cm-1 with B" = 0.076 cm-1 and has been assigned as the A" symmetry, H-F out-of-plane libration fundamental of HF pentamer. Also, structural parameters and harmonic vibrational frequencies are estimated from high-level, first principles calculations for this system.