Leonid A. Surin

Detection of the millimeter wave spectra of the weakly bound complexes 3He–CO and 4He–CO

For the first time, millimeter wave absorption spectra of the van der Waals complexes 3He–CO and 4He–CO were detected in a supersonic jet. Altogether four rotational transitions of 3He–CO and six rotational transitions of 4He–CO were recorded between 110 GHz and 127 GHz with an intracavity spectrometer based on the millimeter wave generator, called OROTRON. The obtained results were included in a global fit together with previously known data enabling a more precise determination of the energy levels of the 3He–CO and 4He–CO complexes. In extremely cold, dark, and dense interstellar clouds the He–CO complex may have astrophysical relevance.

Discovery of the rotational spectrum of the weakly bound complex CO–H2

Rotational transitions of the CO–H2 van der Waals complex have been measured between 108 and 125 GHz in a supersonic jet. Three absorption lines were recorded and assigned as belonging to CO–paraH2 with a new highly sensitive intracavity spectrometer based on the millimeter wave generator, called OROTRON. The results provide confirmation of the recent infrared data of McKellar at 4.7 μm, enabling a more precise determination of the energies of the rotational levels with different parity in the vibrational ground state. The measured millimeter wave transitions provide precise frequencies for an astronomical search of CO–paraH2.

The CO dimer millimeter wave spectrum: Detection of tunneling transitions

A portion of the CO dimer millimeter wave absorption spectrum has been studied by using our highly sensitive intracavity-jet OROTRON spectrometer in the frequency range from 131 to 174 GHz. By varying the CO concentration in the Ne/CO gas mixture feeding the supersonic jet expansion, the effective temperature of the beam could be changed, revealing a correlation between the observed line intensity and the relative energy of the respective lower state energy levels. Using this temperature dependence and the technique of combination differences together with the data from the infrared study of Brookes and McKellar [J. Chem. Phys. 111, 7321 (1999)], out of over 200 observed transitions, a total of 19 lines could be assigned. All assigned millimeter-wave transitions are tunneling transitions. They belong to four subbands, which connect seven lower energy levels with A+ symmetry to ten previously unknown upper energy levels with A− symmetry. The A+ and A− separation signifies the tunneling splitting of the CO ...

Microwave and millimeter wave study of Ortho-N2 states of CO–N2

Microwave and millimeter wave transitions of the CO–N2 complex were investigated using three different instruments, namely, a pulsed molecular beam Fourier transform microwave spectrometer in the frequency region from 4 to 26 GHz, a microwave-millimeter wave double resonance spectrometer in the frequency regions from 8 to 18 GHz for the microwave and 107–118 GHz for the millimeter wave range, and an OROTRON spectrometer in the frequency range from 107 to 132 GHz. Both a- and b-type transitions associated with the ground-state K=0 levels and the lower K=1 levels of the ortho-N2 states, and with rotational quantum number J up to 19, were measured and analyzed. Nuclear quadrupole hyperfine splittings due to the presence of two equivalent 14N nuclei were resolved and analyzed to give additional information about the angular anisotropy of the interaction potential. The nuclear quadrupole coupling constants obtained are χaa=0.196u200a41(52)u200aMHz for K=0 levels, and χaa=−1.0391(17)u200aMHz, χbb=0.0633(17)u200aMHz for the low...

The weakly bound complex CO–orthoD2: Detection of millimeter-wave transitions

For the first time two rotational transitions of the CO–orthoD2 van der Waals molecular complex have been recorded in a supersonic jet and assigned to the two R-branch transitions, R(1) (J,j,l)=2,1,1←1,0,1u2003112u200a806.515(50)u200aMHz, R(2)=3,1,2,←2,0,2u2003119u200a746.484(50) MHz. These transitions were detected with the highly sensitive intracavity spectrometer based on the millimeter wave generator, called OROTRON. Their measured frequencies are in close agreement with the frequency positions predicted from the infrared spectrum, which accompanies the fundamental band of CO in the 4.7 μm region, and which has been published recently by McKellar [J. Chem. Phys. 112, 9282 (2000)]. The millimeter wave transitions will allow a precise determination of the rotational levels with different parity in the vibrational vCO=0 ground state.

Highly sensitive millimetre-wave spectrometer based on an orotron

The design and operation of a gas millimetre-wave spectrometer based on a tunable generator orotron are presented. The absorption cell occupies a part of the high quality (Q approximately=104) orotron Fabry-Perot cavity. The limit of sensitivity gamma min approximately=(3-5)*10-10 cm-1 has been achieved with source frequency modulation at the output band of a receiver of 1 Hz. The narrow spectral width of the orotron radiation (10-15 kHz without locking) provides the Doppler resolution of spectral lines. An absorption signal of gas under investigation is detected by variations of the collector current of the orotron. New results on rotational transition of SiH4 in a vibrational dyad v2/v4 with the absorption coefficient gamma approximately=10-8 cm-1 are briefly given as an illustration of the sensitivity of this spectrometer.

Application of highly sensitive millimeter-wave cavity spectrometer based on orotron for gas analysis

Abstract Highly sensitive millimeter-wave spectrometer based on tunable coherent source—orotron is proposed for detection of molecular compounds in the air and water vapor by observation of their rotational spectra in frequency region 90–150 GHz. High sensitivity of measurements (2–3)×10−10 cm−1 which gives the detection limit better than 1 ppm for wide class of molecules is achieved by the placement of investigated gas into a high quality (Q≈104) orotron Fabry–Perot resonator. The absorption signal is measured simply from variation of orotron current in the collector circuit. The narrow spectral width of orotron radiation (15 kHz) provides Doppler resolution of spectral lines and high selectivity of analysis respectively without any locking by external frequency standard. The spectrometer has relatively simple operation principles taking account its universality. At the first step four compounds, namely methanol, acetone, carbonyl sulfide and carbon monoxide, have been measured in mixtures with water vapor or air.

Monomer counterrotations and tunneling splitting in CO dimer by data of millimeter wave spectroscopy

Analysis of the rotational spectrum of the molecular dimer (CO)2 measured in the millimeter wave range has been performed and four new rotational states are revealed. Three of these states are characterized by almost free rotations of both monomers in the dimer. These states have approximately the same first term σ in the expansion of the rotational energy in powers of the rotational angular momentum J for various values of the momentum projections on the dimer axis (K=0, 1, 2) and various rotational constants B. The intrinsic rotational angular momenta of CO dimers, j1=j2=1, are determined from the σ value. In addition, a state with K=2 is found which corresponds to one of the known shape isomers of (CO)2. The values of the tunneling splitting for each of the new states are determined. The results indicate that previous data on the suppressed tunneling are determined by the asymmetry of internal rotations in the CO monomers rather than by the K value.