The rotational spectrum of Ar-SiH4 and Ar-SiD4

Microwave spectra of Ar-(SiH4)-Si-28, Ar-(SiH4)-Si-29, Ar-(SiH4)-Si-28, and Ar-(SiD4)-Si-28 were recorded using a pulsed molecular beam Fourier transf orm microwave spectrometer. The K = 0 and K = 1 components of the J = 3 <-- 2 through the J = 7 <-- 6 transitions were measured and assigned in the 9- 24 GHz region, For the primary Si-28 isotopic species, Ar-(SiH4)-Si-28 and Ar-(SiD4)-Si-28, a K = 0, A symmetry, a K = 0, F symmetry. a doubly degener ate K = 1, E symmetry; and an l/K-doubled, K = 1, F symmetry rotational pro gression are observed at the approximate to 1 K rotational temperature of t he supersonic expansion. The rotational constants for the K = 0, A state fo r Ar-(SiH4)-Si-28 and Ar-(SiD4)-Si-28 are B = 1700.40624(9) MHz and 1630.68 7073(22) MHz and the centrifugal distortion constants are D-j = 29.089(3) a nd 20.0198(8) kHz and H-j = -1.91(3) and -0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k = 3, are given here and elsewhere. The values of the rotational constants for the K = 0. A, an d F states and for the K = 1, E state are in good agreement with the infrar ed-determined values for Ar-(SiH4)-Si-28. The measured linear Stark effect of the E-state transitions was analyzed to give a dipole moment of 9.24(8) x 10(-32) C.m [0.0277(2) D]. (C) 1999 Academic Press.