Vibrational spectra of La@C60 and Ce@C60 endohedral fullerenes: Influence of spin state multiplicity.

Endohedral fullerenes with paramagnetic encapsulated atoms are new magnetic materials of interest for numerous applications from medicine to quantum computers. An important phenomenon with endohedral fullerenes is the appearance of new vibrational frequencies not associated with empty fullerenes. The vibrational spectra of the lanthanide endohedral fullerenes La@C60 and Ce@C60 in various spin states are calculated using the density functional method. Most of the spectral lines lie in the 300-1600 cm-1range, and their intensities change dramatically depending on the molecule's symmetry and spin state, which are determined by the encapsulated lanthanide atom. The average frequency shift of the carbon cage vibrations caused by spin transition is only 5 cm-1. The calculated frequencies of the coupled "metal-carbon cage" vibrations of the lanthanide endohedral fullerenes La@C60 and Ce@C60 in various spin states lie in the 10-170 cm-1range. The computational results for both the frequencies and intensities of the metal-cage modes depend considerably on the spin state. The changes in these vibrational modes are due to the changes in the molecular symmetry and the metal-carbon bond lengths. Such dependence can be used as a basis for controlling the spin state of metallofullerenes by measuring the vibration frequencies in the far-infrared zone, which could be important for nanoelectronics and quantum informatics.

Resonances and Dissociative Electron Attachment in HNCO.

In a combined experimental and theoretical study, we probe the dissociative electron attachment in isocyanic acid HNCO. The experimental absolute cross section for the NCO^{-} fragment shows a sharp onset and fine structures near the threshold. The autoionizing state responsible for the dissociative attachment is found in both the R-matrix calculation and using analytic continuation in the coupling constant. The involved A^{'} resonance has a mixed π^{*}/σ^{*} character along the dissociating bond and thus combines the effects of nonzero electron angular momentum and dipole-supported states. This leads to unusual behavior of its width at various geometries. Because the potential energy gradient of the autoionizing state points essentially in the direction of the N─H bond, nuclear dynamics can be described by a one-dimensional nonlocal model. The results agree with the experiment both quantitatively and qualitatively. The present system may be a prototype for interpretation of the dissociative electron attachment process in a number of other polyatomic systems.

Laser spark formamide decomposition studied by FT-IR spectroscopy.

High-resolution FT-IR spectroscopy was used for the analysis of the products of formamide dissociation using a high-energy Asterix laser. In the experiment, the detected products of the formamide LIDB dissociation were hydrogen cyanide, ammonia, carbon monoxide, carbon dioxide, nitrous oxide, hydroxylamine, and methanol. The molecular dynamics of the process was simulated with the use of a chemical model. The chemistry shared by formamide and the products of its dissociation is discussed with the respect to the formation of biomolecules.

Dispersion of light and heavy pollutants in urban scale models: CO(2) laser photoacoustic studies.

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO(2) laser photoacoustic spectroscopy in the region of the atmospheric window (9-10 mum). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

GaSb based lasers operating near 2.3 microm for high resolution absorption spectroscopy.

The paper describes results obtained with a new type of GaSb based semiconductor distributed feedback multiple quantum well lasers operating in continuous wave mode well above room temperature. The lasers show good tunability both by current and temperature from 0 to +60 degrees C and current from threshold up to 120 mA. They all operate in high power (1-3 mW) single mode regime and can be tuned in the methane and ammonia overtone absorption spectral range over up to 12 cm(-1) and can be used for the detection of these and other gases.

Laser diode photoacoustic detection in the infrared and near infrared spectral ranges.

A new technique for high resolution photoacoustic detection based on application of laser diodes has been developed. This method was tested and compared using identical photoacoustic instrumentation (cell and microphone) to study gas absorption in three different spectral regions, namely: the infrared range near 2100 cm(-1), CO and OCS fundamental band absorption; the ranges near 4200 and 4350 cm(-1), CH4, NH3 and N2O overtone and combination band absorption; the near infrared range near 6500 cm(-1), CO, CO2 and NH3 overtone absorption. Several types of diode laser operating at room temperature or at liquid nitrogen temperature were compared. The optimum gas pressures for the maximum sensitivity of the photoacoustic signals were found and the detection limits were estimated for all of the gases studied. The best sensitivity was achieved for NH3 at 100 ppbv. The sensitivity of the developed system was tested on detection of traces of NH3 and CO2 gases from car exhaust.

High resolution emission Fourier transform infrared spectra of the 4p-5s and 5p-6s bands of ArH.

In the 2500-8500 cm(-1) region several strong emission bands of (40)ArH were observed by Fourier transform spectroscopy through a dc glow discharge in a mixture of argon and hydrogen. Rotational-electronic transitions of the two previously unstudied 4p-5s and 5p-6s,v = 0-0, bands of (40)ArH were measured and assigned in the 6060 and 3770 cm(-1) regions, respectively. A simultaneous fit of the emission transitions of the 4p-5s and 5p-6s bands and an extended set of transitions of the 6s-4p band observed by Dabrowski, Tokaryk, and Watson [J. Mol. Spectrosc. 189, 95 (1998)] and remeasured in the present work yielded consistent values of the spectroscopic parameters of the electronic states under investigation. In the branch of the 4p-5s band with transitions of type (Q)Q(f(3)e) we observed a narrowing in the linewidths with increasing rotational quantum number N. The rotational dependence of the linewidth is caused by predissociation of the 5s state by the repulsive ground 4s state through homogeneous coupling and changes in overlap integrals of the vibrational wave functions with the rotational level. Analysis was based on the Fermi's golden rule approximation model. In the 4p-5s band region a vibrational sequence ofv(')-v(")=1-1, 2-2, and 3-3 were recorded and a number of transitions belonging to the strongest (Q)Q(f(3)e) form branch of the 1-1 band were analyzed.

Application of InAsSb/InAsSbP and lead chalcogenide infrared diode lasers for photoacoustic detection in the 3.2 and 5 microm region.

An investigation of photoacoustic detection using 3.2-3.6 and 5 mum diode lasers is described. An inexpensive resonant photoacoustic system was developed based, on a simple glass cell and condenser and electret microphone (Brüel & Kjaer type 4144/Sennheiser type K6P). The system was tested on the single rotation-vibration lines of C(2)H(2), CO, COS, and NH(3) gases. The best detection limits obtained are 300 ppm V for C(2)H(2) and 20 ppm V for COS. Potential applications of infrared diode laser photoacoustic detection lie in the areas of analytical chemistry, atmospheric research, and investigation of the kinetics of reactive species.

A tunable single-mode 3.2 microm laser based on an InAsSb/InAsSbP double heterostructure with drive-current tuning range of 10 cm(-1).

A new type of semi-conductor laser with composition InAsSb/InAsSbP is described. This laser was produced for the absorption spectroscopy of atmospherically important molecules in the 3100 cm(-1) region and tested using a closed-cycle He-cryostat in the temperature range 30-80 K. The optimal characteristics of the laser were found to be a heatsink temperature of 62 K and a drive current range of 50-350 mA. Under these conditions, the laser emits single-mode radiation in an exceptionally large wavenumber range of > 10 cm(-1). To test the laser, several experiments were carried out in which the rovibrational absorption spectra of CH3Cl, NH3, OCS and H2O were measured.

Sub-Millimeter-Wave Spectroscopy of the Ar.H+3 and Ar.D+3 Ionic Complexes.

An investigation of the sub-millimeter-wave spectra of the ionic complexes Ar.H+3 and Ar.D+3 is presented. These complexes were produced in a negative glow electric discharge, in mixtures of argon with either H2 or D2. About 80 new transitions were assigned in the 485-680 GHz frequency range using a sub-millimeter-wave spectrometer built with Russian made backward wave oscillators (BWO) sources. These measurements enabled us to observe the first Ka = 2 transitions for Ar.H+3 and the first Ka = 3 transitions for Ar.D+3. Analyses of the line frequencies were carried out using an IAM-like approach, which accounts for the large amplitude internal rotation motion displayed by both species. Insights into the geometry of the intermediate configuration for this large amplitude motion were gained. Copyright 1998 Academic Press.

The Infrared Diode Laser Spectroscopy of the nu2 + nu5 - nu2 Hot Band of Acetylene

The infrared diode laser spectrum of the nu2 + nu5 - nu2 hot band of acetylene has been observed within the discharge plasma of acetylene diluted in He. The concentration of acetylene in the nu2 state was modulated by applying a few kHz of ac current, and the spectrum of the hot band was recorded selectively by the discharge modulation technique. In total, 46 P, R, and Q-branch lines have been assigned to the nu2 + nu5 - nu2 hot band and molecular constants including the band origin 727.59318(27) cm-1 were derived. The lifetime of acetylene in the nu2 state was measured to be about 1 ms, proving that the nu2 state is metastable. The collisional relaxation rate constant of acetylene in the nu2 state by helium was measured to be k = 8.01 ± 0.19 x 10(-14) cm3 molec-1 s-1. Copyright 1998 Academic Press. Copyright 1998Academic Press