Radio-Frequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiDF(3) in the v(6) = 1 Excited State

Rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states: observation of Q-branch perturbation-allowed transitions with delta(k - l) = 0, +/-3, +/-6 and anomalies in the rovibrational structure of the v5 = 1 state

The rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states has been investigated in the centimeter- and millimeter-wave ranges. R-branch (J + 1 <-- J) transitions for J = 0, 1 and Q-branch rotational transitions for the v5 = 1 vibrational state have been measured by waveguide Fourier transform microwave spectroscopy in the range 8-26.5 GHz. The Q-branch transitions include 28 direct l-type doubling transitions (kl = +1, A1) <--> (kl = +1, A2) with J < or = 62, and 108 direct l-type resonance transitions following the selection rule delta k = delta l = +/-2 with J < or = 60 and G = |k - l| < or = 3. A process called "regional resonance" was observed in which a cluster of levels interacted strongly over a large range in J. This process led to the observation of 55 perturbation-allowed transitions following the selection rules delta(k - l) = +/-3, +/-6. In particular, (kl = +1, A+) <--> (kl = -2, A-), (kl = +4, A+) <--> (kl = +1, A-), (kl = +2) <--> (kl = -1), (kl = +3) <--> (kl = 0), (kl = +2) <--> (kl = -3), and (kl = +3) <--> (kl = -3). The various aspects of the regional resonances are discussed in detail. An accidental near-degeneracy of the kl = 0 and kl = -4 levels at J = 26/27 led to the observation of perturbation-allowed transitions following the selection rule delta(k-l) = +/-6 with (kl = +2) <--> (kl = -4). A corresponding near-degeneracy between kl = -1 and kl = -3 levels at J = 30/31 led to the detection of similar transitions, but with (kl = +3) <--> (kl = -3). In the range 230-480 GHz, R-branch rotational transitions have been measured by absorption spectroscopy up to J = 49 in the ground-state and up to J = 50 in the v5 = 1 vibrational state. The transition frequencies have been analyzed using various reduced forms of the effective Hamiltonians. The data for the v5 = 1 vibrational state have been fitted successfully using two models up to seventh order with delta k = +/-3 interaction parameters constrained (dt constrained to zero, and epsilon to zero or to the ground-state value). On the other hand, reductions with the (delta k = +/-1, deltal = -/+2) interaction parameter q12 fixed to zero failed to reproduce the experimental data since the parameters defining the reduction transformation do not arise in the correct order of magnitude. The ground-state data have been analyzed including parameters up to fourth order constraining either parameters of the delta k = +/-3 interactions to zero (reduction A), or of the delta k = +/-6 interactions to zero (reduction B). The unitary equivalence of the different parameter sets obtained is demonstrated for both vibrational states.

High-Resolution Infrared and Millimeter-Wave Study of the Fermi-Coupled v(2) = 1 and v(3) = 2 States of DSiF(3)

The nu(2) (nu(eff.) 854.841 cm(-1)) and 2nu(3) infrared bands (nu(eff.) 840.083 cm(-1)) of DSiF(3) have been studied with a resolution of 2.5 x 10(-3) cm(-1). Moreover, millimeter-wave transitions in the v(2) = 1 and v(3) = 2 states up to J" = 33 have been measured. The assignments and fit of the poorly resolved, compressed cluster-type 2nu(3) IR transitions have been confirmed by a simultaneous study of the 2nu(3)-nu(3) band. The constant W = 5.116 cm(-1) of the Fermi interaction between the v(2) = 1 and v(3) = 2 levels has been determined from frequency effects which are in agreement with relative intensities of the nu(2) and 2nu(3) bands. The deperturbed (B(0) - B(v)) and (C(0) - C(v)) values of the states involved agree with their ab initio predictions within 7% in the worst case. Copyright 2001 Academic Press.

High-Resolution Infrared and Millimeter-Wave Study of the v(3) = 1 State of HSiF(3) and DSiF(3)

Millimeter-wave spectra of HSiF(3) and DSiF(3) in the v(3) = 1 excited state have been measured from 100 to 490 GHz. Infrared spectra have been recorded in the nu(3) regions, nu(0) 424.0301 and 420.9320 cm(-1) in HSiF(3) and DSiF(3), respectively, with a resolution of 2.4 x 10(-3) cm(-1). Since in both species the parameters alpha(B)(3) and alpha(C)(3) have very similar values, no K structure could be resolved in the (Q)P and (Q)R clusters for low-to-medium K values. For high J the effect of the ground state D(JK) term more and more dominates and spreads the J clusters into opposite directions such that medium-to-high K components, particularly those with K = 3p, are resolved. Rotational and infrared data have been fitted together using a model up to sextic centrifugal distortion constants. No perturbations were indicated. Hot bands (nu(3) + nnu(6))-nnu(6) with n = 1, 2, and 3 have been detected and analyzed. Copyright 2000 Academic Press.

Radiofrequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiHF(3): Investigation of the Ground, v(4) = 1, and v(6) = 1 Vibrational States

The present paper deals with the analysis of the microwave, millimeter-wave, and infrared spectra of (28)SiHF(3) in its ground, v(6) = 1 and v(4) = 1 excited states. The former was observed up to 1055 GHz leading to the determination of one octic centrifugal distortion constant, L(J) = -0.0749(55) µHz. Furthermore the <k ||H ||k +/- 6> interaction term ||h(3,GS) || = 1.1032(70) mHz has been fitted from splittings of six K = 3 lines. The excited states have been regarded as isolated ones. This enabled fits according the Q-, D-, and QD-reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and further developed by J. K. G. Watson, C. Gerke, H. Harder, and K. Sarka, (J. Mol. Spectrosc. 187, 131-141 (1997)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)). A multiple fit analysis was performed confirming the assumption that the excited states are not affected by intervibrational resonances. Finally the millimeter spectrum of (29)SiHF(3) and (30)SiHF(3) in their ground state was also measured up to 460 GHz and accurate rotational and centrifugal distortion parameters were derived. Copyright 2000 Academic Press.

Rovibrational Spectroscopy of the v(5) = 1 Level of (28)SiDF(3)

The nu(5) fundamental band of trifluorosilane-d (SiDF(3)) at 627 cm(-1) was studied for the first time by high-resolution FTIR spectroscopy at a resolution of 2.4 x 10(-3) cm(-1). The analysis was performed simultaneously with available microwave and newly measured submillimeter-wave data in the approximation of an isolated degenerate fundamental level of a C(3 Kv) symmetric top molecule leading to a standard deviation of 0.22 x 10(-3) cm(-1) for the reproduction of the infrared wavenumbers, 36 kHz for the microwave, and 198 kHz for the submillimeter-wave frequencies, respectively. The unitary equivalence between the two reductions (Q and D) of the effective Hamiltonian applied in the analysis is demonstrated. Copyright 2000 Academic Press.