Robert L. DeLeon

Stark, Zeeman, and hyperfine properties of v=0, v=1, and the equilibrium configuration of hydrogen fluoride

Molecular beam electric resonance spectroscopy has been done on the v=0 and v=1 states of hydrogen fluoride in external electric and magnetic fields. The v=1 state was populated using a color center laser. v=0, v=1, and equilibrium configuration results have been obtained for the HF dipole moment, fluorine and proton spin rotation interactions, fluorine and proton magnetic shielding anisotropies, both direct and indirect spin–spin interactions, rotational magnetic moment, and magnetic susceptibility. All of these properties can be extrapolated to v=2 with high accuracy and to higher states with reasonable confidence. First and second derivatives with respect to internuclear distance have also been obtained for several of these properties. Comparisons of HF and DF dipole moments indicate significant differences arising from Born–Oppenheimer breakdown.

Vibrational predissociation in the hydrogen fluoride dimer

A color center IR laser was used to excite the proton‐accepting monomer of a HF dimer in a molecular beam. The maximum excess linewidth arising from vibrational predissociation was 10 MHz, indicating a vibrational predissociation lifetime of ≥30 ns. The maximum lifetime was estimated to be 300 ns from intensity considerations.

Molecular beam electric resonance study of the ground and excited states of cyanoacetylene

Cyanoacetylene was studied using molecular beam electric resonance spectroscopy. Ground state results are μ=3.731 72 D, eQq=−4319.24 kHz, CN=0.976 kHz. Zero field spectra were observed for the three singly excited bending modes and Stark data were taken for the lower energy of two of these three states. Excited state results include ν7; μ=3.7225 D, eQqaa=−4302.0 kHz, eQ(qbb−qcc)=−28.8 kHz, CN(J=2)=1.47 kHz; ν6; μ=3.7263 D, eQqaa=−4369.7 kHz, eQ(qbb−qcc)=177.1 kHz, CB(J=2)=1.30 kHz; ν5; eQqaa=−4325.7, eQ(qbb−qcc)=96.8 kHz, CN(J=2)=1.33 kHz. l‐doubling constants were also obtained for the degenerate vibrations.

The vibrational dipole moment function of HCN

Dipole moment measurements for the 100 and 011 excited vibrational states of HCN are presented. These, and previously measured, dipole moments are combined with infrared intensity measurements to obtain dipole moment functions for HCN in both normal and internal coordinate systems. The dipole moment results are 〈 μ〉100=2.980 53(6), 〈 μ〉011=2.976 9(7), and μe =3.016 D. The first dipole derivatives with respect to normal coordinates, from IR intensities, are μ1=+0.0029, μ2=+0.178, and μ3=+0.1111 D. These results plus the vibrational dependence of the dipole moments give the following second derivatives: μ11=−0.003 38, μ22=−0.0251, μ33=+0.0012 D. Dipole moments of several states of DCN are calculated and are in excellent agreement with experimental results.

Structure, properties, and inversion of the Ar⋅SO2 van der Waals molecule

Microwave and radiofrequency spectra of the Ar⋅SO2 van der Waals molecule have been studied by molecular beam spectroscopy. The molecule has Cs point group symmetry and tunnels through a very low barrier at a C2v structure at a 980 MHz rate. The tunneling interchanges the two oxygen atoms which causes half of each inversion doublet to have zero statistical weight. The inversion frequency and assumptions about the bending vibration lead to a barrier height of ?10 cm−1. Stark effect measurements give μa=0.2674 D, μb=0.0 D, μc=1.465 D. These moments are interpreted in terms of a vibrational amplitude of 24° associated with the inversion coordinate. The geometry of the complex is essentially perpendicular with the Ar atom above the plane of SO2 and located almost directly over the SO2 center‐of‐mass at a 3.675 A distance.

Radiofrequency spectroscopy of DCCD: Deuterium quadrupole coupling in acetylene☆

Abstract Molecular beam electric resonance spectroscopy has been used to observe the P (16) e and P (16) f transitions in the ν 5 - ν 4 band of dideutero acetylene. Hyperfine transitions were resolved in the P (16) e case, providing deuterium quadrupole coupling and spin rotation information. The hyperfine properties are essentially the same for ν 4 , J = 16 and ν 5 , J = 15 with eQq = 209(1) kHz and C = −0.42(2) kHz. This information is compared with other measurements of deuterium quadrupole coupling in acetylene.

Electric dipole moment and hyperfine properties of bromoacetylene in the ground and first excited C–H stretching vibrational states

Molecular beam electric resonance spectroscopy, combined with color center laser excitation, has been used to measure the electric dipole moment and Br hyperfine properties of bromoacetylene in its ground and first excited C–H stretching vibrational states. For the HCC79Br, v=0: μ=0.229 62(1) D, eQq=648.113(3) MHz, CBr=6.4(3) kHz, and B=4000.07 MHz. For the HCC79Br, v=1: μ=0.248 82(1) D, eQq=648.160(2) MHz, CBr=7.0(3) kHz, and B=3992.79 MHz. For the HCC81Br, v=0: μ=0.229 56(1) D, eQq=541.430(1) MHz, CBr=7.4(1) kHz, and B=3978.46 MHz. For the HCC81Br, v=1: μ=0.248 61(1) D, eQq=541.464(3) MHz, CBr=7.6(4) kHz, and B=3971.34 MHz. The vibrational band origin for the C–H stretching vibration is 3367.7(2) cm−1.

Vibrational relaxation of linear molecules in a nozzle expansion

Abstract Vibrational relaxation in a supersonic nozzle expansion has been investigated for the case of linear molecules seeded in argon, expanded through a 25 μm diameter aperture. Electric resonance spectroscopy was used to obtain vibrational temperatures for 13 different vibrational states in OCS, HCN, and cyanoacetylene. No significant vibrational cooling was observed for modes with vibrational frequencies greater than 500 cm−1.

Molecular-beam studies of Van der Waals complexes of atmospheric interest

The radio-frequency and microwave spectra of the Ar·O3 and Ar·SO2 Van der Waals complexes have been analysed with the conventional first-order centrifugal distortion Hamiltonian plus inversion and centrifugal distortion of the inversion frequency. The centrifugal distortion constants were then used to obtain a force field describing the Van der Waals vibrations. This procedure worked quite well for Ar·O3, generating vibrational properties appropriate for a semi-rigid complex. Ar·SO2, however, cannot be described by such a harmonic model. Ar·SO2 has a very isotropic Van der Waals potential where stretching and bending vibrations are strongly coupled. In addition, a qualitative study of many SO2-containing bimolecular complexes was made. It was possible to categorize these complexes as having strong, moderate or weak interactions.

Stark and hyperfine properties of oxygen difluoride

Radio frequency transitions within six different rotational levels of oxygen difluoride have been observed in the presence of external electric fields. These data were analyzed in terms of the dipole moment, polarizability anisotropies, spin rotation, and spin–spin interactions: μ=0.308 18(3) D, αaa−αbb=1.389(8) A3,αaa−αcc=1.883(10) A3, Maa=59.60(7) kHz, Mbb=25.05(11) kHz, Mcc=51.39(8) kHz, and 〈1/R3〉=0.0941(5) A−3.