H.E. Radford

Analysis of the laser magnetic resonance spectrum of HO2

An analysis of the previously detected laser magnetic resonance spectrum of HOt is carried out by (i) assigning MJ quantum numbers to each observed Zeeman line, (ii) determining the quantum numbers (N‘K”K,’-N’’K,,,K,’,) and energies of the zero-field asymmetric rotor transitions involved, and (iii) determining the values of the zero-field spin-rotation doublet splittings in the upper and lower states of each asymmetric rotor transition. The rotational transitions obtained lie in the region 50-150 cm-’, with quantum numbers 4 5 N 5 19 and 1 < K, 5 4. They are fit to an asymmetric rotor program to obtain the three rotational constants A, B, C and the three symmetric-top centrifugal distortion constants DK, DNK, DN. The spin splittings are fit to an approximate theoretical expression involving two adjustable linear combinations of components of the spin-rotation interaction tensor E. Because of the lack of spectra from other isotopic species, a unique molecular geometry cannot be derived.

The rotational spectrum of trans-HOCO and DOCO

Part of the rotational spectrum of the hydroxyformyl radical, HOCO, and its deuterated analog has been detected at frequencies between 230 and 300 GHz. The radical was formed in a flow system by the reaction between chlorine atoms and formic acid. Analysis of the spectra yields reliable estimates of the rotational, centrifugal distortion and spin–rotational parameters describing the ground state of this species. The rotational constants derived for HOCO and DOCO are consistent with a planar equilibrium structure and are used to confirm that the carrier of the spectrum is the trans‐geometrical isomer.

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°.

b‐dipole transitions in trans‐HOCO observed by far infrared laser magnetic resonance

Far infrared laser magnetic resonance spectroscopy is used to measure components of 12 rotational transitions in the ground state of the HOCO radical. The transitions are all b‐dipole in character in contrast to the a‐dipole rotational spectrum previously reported [Radford, Wei, and Sears, J. Chem. Phys. 97, 3989 (1992)]. The new data determine the A rotational constant to high precision and allow the determination of several centrifugal distortion constants for the first time. The hyperfine coupling in the radical leads to observable splittings in several of the observed transitions and these are used to estimate two of the four expected nonzero hyperfine parameters in the radical.

Pressure broadening of millimeter-wave ozone lines by atmospheric gases

Abstract Pressure-broadened linewidths of the 4 13 -4 04 , 6 15 -6 06 , 14 3 11 -15 2 14 , and 28 5 23 -29 4 26 rotational transitions of ozone have been measured for the foreign gases N 2 and O 2 over a pressure range of 200–1000 m Torr. The temperature dependence of the broadening has been measured for the 4 13 -4 04 and 6 15 -6 06 transitions over the range 195–320 K. The air-broadened linewidth of the 6 15 -6 06 transition was measured at 294 K and is readily calculated for other temperatures and transitions from the N 2 and O 2 results. The results are compared with recent theoretical calculations, and also with previous measurements, where these are available. The measurements have direct application to the interpretation of observations of microwave emission of middle atmosphere ozone. The results also serve as reference points for theoretical linewidth calculations applicable from the microwave to the infrared spectral regions.

Avoided crossings in the far-infrared laser magnetic resonance spectrum of HCO

Abstract Several transitions in the far-infrared spectrum of the HCO radical have been detected by the technique of laser magnetic resonance (LMR). The spectra have been assigned to both a- and b-dipole transitions and have been fitted together with previous microwave, millimeter-wave, and infrared measurements to determine a full set of parameters for HCO in its ground state. In particular, signals arising from the avoided crossing of the levels 808 and 716 in a magnetic field have been analyzed and used to determine values for the off-diagonal components of the spinrotation, proton dipolar hyperfine, and anisotropic g-tensors which are responsible for the mixing of the states. The reduced spin-rotation parameter ( ϵ ab + ϵ ba ) has been separated into its component parts by the imposition of the constraint ϵ ab ϵ ba = A B .

Laser magnetic resonance measurement of rotational transitions in the metastable a1Δg state of oxygen

Abstract Laser magnetic resonance (LMR) for five rotational transitions, J = 4 ← 3, 5 ← 4, 7 ← 6, 8 ← 7, 9 ← 8, of the oxygen molecule 16 O 16 O in its metastable state, a 1 Δ g , v = 0, are observed using six fir laser lines. Taking the known values of the g factors, their zero-field frequencies are obtained as 340.0085(6), 424.9810(9), 594.870(1), 679.780(1), and 764.658(1) GHz, respectively. They are fit by ( E h ) = B 0 [J(J + 1) − 4] + D 0 [J(J + 1) − 4] 2 + (−1) J ( 1 2 )qJ (J + 1)[J(J + 1) − 2] , where B 0 = 42.50457(10) GHz, D 0 = 153.14(110) kHz, and q = 0.050(90) kHz.

Far infrared laser magnetic resonance spectra of the ClSO and FSO radicals in the gas phase

Abstract The detection of the free radicals ClSO and FSO by the technique of far infrared laser magnetic resonance is reported. Observations of the former have been made with several laser lines; the spectra are complicated and have not been assigned but are attributed to ClSO on the basis of several chemical tests. The FSO radical was generated by the reaction of carbon disulphide with the products of a discharge through CF4 + O2. Spectra have been observed with laser lines at 394, 419 and 513 μm. Using the results of a subsequent microwave study of FSO, the rotational transitions involved in these spectra have been identified. The spectrum at 513 μm has been studied in detail and is shown to arise through level anticrossings between the levels 145,Kc (the lower levels involved in the transition) and 154,Kc+2. All aspects of this spectrum are reproduced quantitatively by the parameters determined from the microwave spectrum. It is thought that the other two FSO spectra arise in a similar manner. Such anticrossing signals are likely to be widespread in LMR experiments, causing intense narrow lines to occur at high magnetic fields even for molecules with weakly coupled electron spin.