D. A. Fletcher

A supersonic molecular beam optical Stark study of CaOH and SrOH

The permanent electric dipole moments of CaOH and SrOH in their X 2Σ+, A 2Π3/2, A 2Π1/2, and B 2Σ+ states have been measured using the technique of supersonic molecular beam optical Stark spectroscopy. For CaOH the values obtained were μ(X 2Σ+)=1.465(61)D, μ(A 2Π1/2)=0.836(32)D, μ(A 2Π3/2)=0.766(24)D, and μ(B 2Σ+)=0.744(84)D, while for SrOH the values were μ(X 2Σ+)=1.900(14)D, μ(A 2Π1/2)=0.590(45)D, μ(A 2Π3/2)=0.424(5)D, and μ(B 2Σ+)=0.396(61)D. The results are compared with values from a recent ab initio calculation for CaOH and with the predictions of a semiempirical electrostatic polarization model.

Hyperfine interactions in the ground states of titanium monoxide and mononitride

A comparative study of the hyperfine interactions in the X 2Σ+ state of TiN and the X 3Δ state of TiO has been performed. The 48Ti14N(I=1) hyperfine structure was determined from the analysis of 19 components of the N=1–0 and N=2–1 pure rotational transitions recorded using the pump/probe microwave‐optical double resonance technique. The 47Ti(I=5/2) hyperfine structure of X 2Σ+ TiN was determined from an analysis of the high resolution optical spectrum of the (0,0) A 2Π3/2–X 2Σ+ band system. The resulting parameters are (in MHz) B(48Ti14N)=18 589.3513(13), D(48Ti14N)=0.026 31(18), γ(48Ti14N)=−52.2070(13), bF(N)=18.480(3), c(N)=0.166(7), eQq0(N)=−1.514(8), CI(N)=0.0137(12), bF(47Ti) =−558.8(11), c(47Ti)=−15(5), and eQq0(47Ti)=62(16). An analysis of the (0,0) band of the B 3Π–X 3Δ system of 47Ti16O produced the X 3Δ hyperfine parameters (in MHz): a(47Ti) =−54.7(21), (bF+2c/3)(47Ti)=−231.6(60), and eQq0(47Ti)=−49(31). An interpretation based upon the predicted nature of the bonding in TiO and TiN is given.

Millimeter‐wave spectroscopy of vibrationally excited ground state alkaline‐earth hydroxide radicals (X 2Σ+)

Pure rotational spectra of the alkaline‐earth monohydroxides have been recorded for vibrationally excited states (0 1 0), (0 2 0), (0 3 0), and (1 0 0) of the ground electronic state (X 2Σ+) using millimeter‐wave absorption spectroscopy. The radicals MgOH, CaOH, SrOH, and BaOH were studied. The data for CaOH, SrOH, and BaOH were analyzed with a linear 2Σ+ model, but with the addition of two terms to account for contamination of the v2=1 2Π and v2=2 2Δ vibronic levels with 2Π and 2Δ electronic states. The data for MgOH, however, did not fit well to this linear model and is additional evidence that this species is quasilinear.

MOLECULAR BEAM PUMP/PROBE MICROWAVE-OPTICAL DOUBLE RESONANCE USING A LASER ABLATION SOURCE

The first successful pump/probe microwave‐optical double resonance experiment using a laser ablation/reaction scheme for molecular beam production has been performed. Pure rotational transitions at frequencies up to 52 GHz have been recorded for the transient refractory compounds YF, YO, and SrOH at a resolution of <30 kHz [full‐width at half‐ maximum (FWHM)]. The observed three lowest pure rotational transition frequencies of YF (X 1Σ+) were analyzed to produce an improved set of rotational constants, B=8683.6156(11) MHz and D=0.007 521(74) MHz. The three lowest pure rotational transitions of SrOH (X 2Σ+) were analyzed to give the spectroscopic parameters (in MHz), B=7470.8180(4), D=0.006 25(3), γ=72.706(1), γD=−0.0021(2); bF (H)=1.713(2) and c (H)=1.673(5). The proton magnetic hyperfine interactions were interpreted in terms of a molecular orbital description for the X 2Σ+ state.

Molecular beam optical Stark spectroscopy of calcium monocyanide

The 617.7 and 614.7 nm bands of calcium monocyanide, CaNC/CaCN, have been recorded at high resolution by laser‐induced fluorescence using a supersonic molecular beam. The two bands consist of twelve branches that are assigned to a case a (0,0,0)A 2Πr–(0,0,0)X 2Σ+ transition. A reduction of the data to an effective Hamiltonian model produced the spectroscopic parameters (cm−1): T00= 16229.5417(26), B″=0.13499(14), γ″=6.1837(33)×10−4, A′=77.6451(40), B′=0.15027(23), AD′=2.69(11) × 10−3, D′= −3.50(25) × 10−5, p′=0.0754(18), q′=−0.04808(87), qD′′= 2.64(65) × 10−5. It is proposed that the anomalous values of the excited state parameters arise because of Renner–Teller interactions. The magnitude of the permanent electric dipoles, |μ|, were also determined and are 5.949(1) D[A 2Π1/2(0,0,0),J= 0.5] and 6.895(9) D[X 2Σ+(0,0,0),J= 1.5]. The large value of |μ| is consistent with an isocyanide structure, CaNC. A comparison with theoretical predictions is presented.

Molecular beam optical Stark spectroscopy of MoN

The rotationally resolved spectrum of the (000–000) B 2A‘–X 2A’ band system [T000–000=15 859.4638(15) cm−1] of a supersonic molecular beam sample of calcium monohydrosulfide, CaSH, was recorded in the presence of a variable static electric field. The magnitude of the a‐principal axis component of the permanent electric dipole moment, ‖μa‖, was determined to be 5.36(4) and 3.78(7) D for the X 2A’ and B 2A‘ states, respectively. An analysis of the field free spectra produced values for the (000) B 2A‘ vibronic state fine structure parameters of (in cm−1); A’=10.433 56(16), B’=0.143 43(15), C’=0.141 14(15), eaa=−5.779 3(19), ebb=0.107 67(88), and ecc=0.032 70(83). An interpretation of the parameters is presented.

Refractory radicals generated by pick-up molecular beam techniques

Abstract A new method of the generation of “cold” molecular beam samples of high temperature refractory compounds is described. The method combines the simplicity of an electron bombardment effusive oven for the generation of refractory compounds with the advantage of supersonic expansion. The applicability of the technique is de monstrated by recording the high-resolution laser-induced fluorescence (LIF) spectra of the (0, 0) B 2Σ+−X 2Σ+ (ν00=16855.14 cm−1) band system of CaCl. A comparison with the LIF spectra for a molecular beam sample of CaCl generated by conventional effusive oven techniques is made.