A. Dymanus

Observation of far-infrared transitions of HCO+, CO+ and HN+2

Abstract Rotational transitions of molecular ions HCO + , CO + , and HN + 2 have been observed at frequencies aroud 1 THz. The ions were produced in the negative glow of a hollow cathode discharge cooled by liquid nitrogen. Preliminary results indicate efficient production of ions in an absorption cell of simple construction.

High-resolution molecular-beam spectroscopy of NaCN and Na13CN

Abstract The sodium cyanide molecule was studied by molecular-beam electric-resonance spectroscopy in the microwave region. We used the seeded-beam technique to produce a supersonic beam with strong translational, rotational and vibrational cooling. In the frequency range 9.5–40 GHz we observed and identified for NaCN 186 and for Na13CN 107 hyperfine transitions in 20 and 16 rotational transitions, respectively, all in the ground vibrational state. The rotational, the five quartic and three sextic centrifugal distortion constants of NaCN are: A″ = 57921.954(7) MHz; B″ = 8369.312(2) MHz, C″ = 7272.712(2) MHz. All quadrupole and several spin-rotation coupling constants for the hyperfine interaction were evaluated. The quadrupole coupling constants (in MHz) for NaCN are: eQq12(Na) = −5.344(5), eQq12 = 2.397(7). eQq12(N) = 2.148(4), eQq12(N) = −4.142(5). From these constants and those of Na13CN we have determined the principal components of the quadrupole coupling tensor for potassium and nitrogen. The structure of sodium cyanide evaluated from the rotational constants of NaCN and Na13CN was found to be T shaped, similar to the structure of KCN but completely different from the linear isocyanide configuration of LiNC. The effective structural parameters for sodium cyanide in the ground vibrational state are: rCN = 1.170(4) A, rNaC = 2.379(15) A, rN12N = 2.233(15) A, in gratifying agreement with ab initio calculations. Both the geometrical structure and the hyperfine coupling justify the conclusion that the CN group in gaseous sodium cyanide approximately can be considered as a free CN− ion.

Rotational spectrum, hyperfine spectrum and structure of lithium isocyanide

Abstract The rotational spectrum of LiNC has been measured for the first time. We succeeded in producing a supersome molecular beam (= 1% LiNC in Ar). The molecular-beam electric-resonance technique has been employed to obtain high-resolution microwave spectra. Two rotational transitions ( J = 1 → 0 and J = 2 → 1) of 7 LiNC in the ground vibrational state were observed. The hyperfine structure was resolved and identified with the help of microwave-microwave double resonance. The rotational constants B 0 and D 0 and the hyperfine coupling constants eQq (Li), eQq (N), and c (Li) could be deduced. The J = 1 → 0 rotational transition of 6 LiNC was observed in natural abundance. From this we conclude that LiNC has a linear isocyanide structure. The results for the effective structural parameters are: r LiN = 1.760 A, and r NC = 1.168 A. We did not observe transitions in excited vibrational states or from LiCN. The agreement between the experimental results and recent ab initio calculations is good.

A far infrared laser sideband spectrometer in the frequency region 550–2700 GHz

This paper describes a tunable far‐infrared (FIR) spectrometer. Tunable radiation is obtained by frequency mixing, fixed frequency FIR laser radiation and tunable microwave radiation in Schottky barrier diodes. An optically pumped laser and an HCN discharge laser are used as FIR sources and klystrons in the frequency range of 22–114 GHz as microwave sources. This yields an 85% coverage of the frequency region between 550 and 2700 GHz. Up to sixth order sidebands have been generated and used for spectroscopy. The ultimate sensitivity corresponds to a minimum detectable fractional absorption of 10−5 at 1‐s RC time. The applicability of the spectrometer in high‐resolution spectroscopy of transient species has been demonstrated by the observation of spectra of OD and N2H+. New laser emissions of optically pumped CH2F2 have been found and accurate frequencies have been determined for some of them.

Rotationally resolved laser spectroscopy of tetracene and its van der Waals complexes with inert gas atoms

By using a molecular beam apparatus in combination with a single frequency dye laser we were able to resolve several rovibronic bands in the S1 electronic state of tetracene (C18H12) and its van der Waals complexes with inert gas atoms. The spectra of tetracene have been assigned and rotational constants were derived for the S0 and S1 electronic state. The existence of perturbations in the rotational spectra of the van der Waals complexes is demonstrated.

High resolution laser spectroscopy on the c1P - a1D transition in NH

Abstract The spectrum of the c 1 Π, v = 0 ← a 1 Δ, v = 0 band of the NH molecule at λ = 324 nm has been investigated under high resolution by laser-induced fluorescence in a molecular beam. From an analysis of the spectra we obtained: the magnetic dipole interaction constants a N,H and the electric quadrupole constants eQq 1,2 for both electronic states, the improved values for the Λ-doubling constants q π , q π D , and q π H for the c 1 Π state, and rotational constants for both electronic states up to a third-order centrifugal distortion. Also, the Λ-doubling in the a 1 Δ state could be determined.

Hyperfine structure and Lifetime of the C2S+ state of CH

From a laser induced fluorescence (LIF) experiment on a molecular beam of CH, we have obtained the b and c hyperfine constants, the γ and γD spin‐rotation constants as well as accurate values for the rotational constants B, D, and H for the C 2Σ+, v=0 state. From measurements of the linewidths, that are partially caused by predissociation, and by comparing relative line intensities, we determined different lifetimes for upper (F1) and lower (F2) ρ‐doublet states of the C 2Σ+ state. For the F1 states we find a constant lifetime of 3.7±1.0 ns, that is independent of N, while for the F2 states we observed an increase in lifetime for higher N up to 8.0±1.5 ns for N=11.

High resolution molecular beam spectroscopy on the A2S+, v=0 state of SH

Abstract In a molecular-beam laser-induced fluorescence experiment on SH, the hyperfine and spin—rotation structure in the A 2 Σ 1/2 + , ν=0 state has been determined. From linewidth measurements, a rotationally dependent predissociation is shown to be present. A natural lifetime of 3.2 ± 0.3 ns is obtained for N =0.

Far infrared laser sideband spectroscopy of H3O+: the pure inversion spectrum around 55 cm−1

Abstract We have observed twenty pure inversion transitions in the vibrational ground state of H 3 O + in the frequency region around 55 cm -1 . Spectra were recorded with a FIR laser sideband spectrometer. Analysis required the inclusion of Δ k = ± 3 n interactions in the Hamiltonian and yielded an improved set of molecular parameters for the vibrational ground state. Predictions are made for the frequencies and intensities of forbidden transitions in the FIR region.

Submillimeter spectroscopy on OH+: The rotational transition at 1 THz

A report is presented of the first observation and complete analysis of the spin multiplet and hyperfine structure of the lowest rotational transition (N = 0 to 1) in the X 3 Sigma -, v = 0 ground state of the hydroxyl cation OH(+). The discussed study provides molecular constants for the ground state and yields accurate frequencies for the lowest transitions which may facilitate detection of OH(+) in interstellar clouds. The observed spectrum has been fitted to an appropriate Hamiltonian describing the rotational and fine structure and the magnetic hyperfine structure of a 3 Sigma state. 12 references.