John M. Brown

A determination of fundamental Zeeman parameters for the OH radical

Measurements of the gas-phase E.P.R. spectra of OH in the J = 9/2 and 11/2 levels of the X2II state at 26 GHz and 35 GHz respectively are reported. Confocal and semi-confocal optical resonators have been used in place of the more conventional microwave cavities for these experiments. The data are analysed, together with previous measurements by Radford on other rotational levels in the determination of six independent g factors: These parameters are interpreted in terms of the electronic structure of the OH radical. In agreement with previous workers, it is found that the major contaminant of the X2II state is the A2Σ+ state and that this pair of states is a good example of Van Vlecks pure precession hypothesis.

The rotational spectrum and hyperfine structure of the methylene radical CH2 studied by far-infrared laser magnetic resonance spectroscopy

Thirteen pure rotational transitions of CH2 in its X 3B1 ground vibronic state have been measured and assigned using the technique of far‐infrared laser magnetic resonance (LMR) spectroscopy. The energy levels thus determined led to the prediction and subsequent detection by microwave spectroscopy of a further rotational transition 404–313, at lower frequency (∼70 GHz). The analysis of these observations yields precise rotational constants as well as spin–spin, spin‐rotation, and hyperfine interaction parameters for gas phase CH2. Its rotational spectrum may enable interstellar CH2 to be detected by radio astronomy. Two rotaional transitions within the v1=1 excited vibrational state have also been identified in the LMR spectrum. Future observations of vibrationally excited CH2 may afford a means of determining the singlet–triplet splitting in methylene, and studies of CD2 and CHD will result in improved structural determinations.

The far-infrared Laser Magnetic Resonance Spectrum of the OH radical

Abstract The far-infrared Laser Magnetic Resonance (LMR) Spectrum of the OH radical in the v = 0 level of the X2Π state has been studied in detail. All transitions that are accessible with currently available laser lines have been recorded. The measurements have been analyzed and subjected to a single least-squares fit using an effective Hamiltonian. The data provide primary information on the rotational and fine-structure intervals between the lowest rotational levels and the parameter values determined in the fit are A 0 = −4168.63913(78) GHz , γ 0 = −3.57488(49) GHz , B0 = 555.66097(11) GHz, D0 = 0.0571785(86) GHz.

The EPR and LMR spectra of the DO2 radical: Determination of ground-state parameters

Abstract The detection of lines in both the gas phase EPR spectrum at 9 GHz and the far-infrared LMR spectrum of the DO2 radical is reported. The measurements are fitted with an appropriate Hamiltonian and several parameters for the molecule in the X 2 A″ state are determined. The majority of the transitions in the EPR spectrum are K-type doubling transitions and involve the a-component of the electric dipole moment. However the observation of one b-type transition (505-414) permits the determination of the off-diagonal component of the spin-rotation tensor, ϵab, and an estimate of the relative magnitudes of the a- and b-components of the dipole moment. A combination of the parameters for HO2 with those for DO2 leads to a better understanding of the properties of the molecule. In particular, the r0 molecular geometry has been determined more reliably than previously to be r 0 (OH) = 0.9774 A , r 0 (OO) = 1.3339 A , ∠HOO = 104.15°.

Anharmonic corrections for linear triatomic molecules subject to the Rennet-Teller effect

The effects of vibrational anharmonic terms and of the gK -correction on the energy levels of a triatomic molecule in a degenerate electronic state are considered. The electronic wavefunctions are described using the approach first suggested in the original paper of Renner. Formulae for the anharmonic corrections in a number of different situations are derived. For an electronic Π state the corrections are given in the form where i runs over the various contributions and x 1, x 2, … depend on the anharmonic force constants. The functions Fi can be determined numerically (see equations (4.3) and 4.7)). For the case without spin-orbit interaction the Fi s are given explicitly to first order in ∈ in table 1. Further-more, the same results apply for levels with |K|=v 2+1 even if the spinorbit interaction is not negligible. Explicit results for levels with |K|<v 2 including spin-orbit interaction are given in tables 2 and 3. The cases with larger values for Λ (2, 3, …) are also considered. The energy level for...

The electron resonance spectra of BrO, IO and SeF in J=5/2 rotational levels

The electron resonance spectra of BrO, IO and SeF in the J = 5/2 rotational levels of their ground 2II states have been observed and analysed. Comparison of these results with those obtained in the J = 3/2 levels leads to values for corrections to the magnetic moment arising principally from third-order effects of the spin-orbit coupling.

The laser magnetic resonance spectrum of the NCO radical at 5.2 μm

Abstract Lines in the ν 3 (“antisymmetric” stretch) fundamental of the NCO radical in the X 2 Π state were studied by CO laser magnetic resonance. The observations were assigned to P and R lines in the vibration-rotation band and lead to a precise determination of the vibrational interval and the anharmonic correction to the rotational constant: ν 3 = 1920.60645(19) cm −1 , α 3 = 0.003338(21) cm −1 . A single transition in the hot band (011)-(010), 2 Δ 5 2 - 2 Δ 5 2 was detected. This observation is used to determine the origin of the hot band as 1907.11892(20) cm −1 , i.e., the anharmonicity parameter x 23 = −13.48753(28) cm −1 .

Magnetic dipole transitions in the far infra-red spectrum of nitric oxide

Rotational lines in the far infra-red spectrum of nitric oxide corresponding to direct transitions between the two spin components of the ground 2II state have been observed. Intensity calculations show that these lines arise from magnetic dipole transitions between the two spin components. Analysis of the spectrum leads to a direct determination of the value for the spin-orbit coupling parameter A 0 of 123·16±0·02 cm-1. In addition, the pure rotational spectrum of nitric oxide has been extended to higher J values.

The laser magnetic resonance spectrum of the ν2 band of NH2

Abstract The ν 2 fundamental band ( ν 0 = 1497.3 cm −1 ) of the NH 2 radical was studied by CO laser magnetic resonance. The NH 2 radicals were produced by the reaction of hydrated hydrazine and hydrogen atoms obtained from a discharge in water vapor. The assignment was established for about 160 Zeeman resonances which involved levels with 0 ≦ N ≦ 7 and 0 ≦ K a ≦ 5. From an analysis of the observed spectra, combined with the previously reported 10 μm and far infrared LMR spectra, the band origin, the rotational, the centrifugal distortion, and the spin-rotation constants were accurately determined both for the ν 2 = 1 and the ground states. As in the case of HCO, large changes of A , Δ K , ϵ aa , and Δ K s were observed upon the excitation of the ν 2 mode.

Determination of the dipole moment of the amino radical by optical Stark spectroscopy with a tunable dye laser

Stark effects have been observed for individual lines in the excitation spectrum of the NHD radical, recorded in the visible region with a tunable dye laser. Even though the spectra have been studied with Doppler limited linewidths, it has been possible to resolve individual MJ components. The results are interpreted in terms of an interaction between the applied electric field and the dipole moment of the molecule in the ground state (predominantly involving the a component) and yield a value for μ of 1·82±0·05 D. The experiments performed on transitions to the (0, 9, 0) level of the A 2 A′ state suggest that there is a significant contribution to the Stark effect from the molecule in the upper state also; the a component of the dipole moment involved is measured to be 0·19±0·06 D. Possible explanations of the origin of this dipole moment are discussed.