The stratospheric aerosol sulfate layer (Junge layer) may influence the earth's radiation budget, climate, and stratospheric ozone levels. In this paper, we present research activities at the National Center for Atmospheric Research employing high resolution tunable diode laser absorption spectroscopy which address two separate aspects of the Junge layer: laboratory heterogeneous measurements of reaction probabilities between stratospheric gases of importance and aqueous H₂SO₄ aerosols, and studies of OCS sources, sinks, and potential long-term secular trends.

By use of techniques which we have developed over the past few years, it is now possible to experimentally measure pressure broadening parameters over a three decade range of temperature, including the very low temperature regime in which most spectroscopically active gasses have vanishingly small vapor pressures. As a result, collisional processes can be considered in a manner analogous, albeit at a lower resolution, to that of the more familiar energy level spectroscopy.

The dynamic analysis provides deep insight of the motion regularity or stochastity, the energy regions where transitions between these types of dynamics take place, specific features of the molecular states in different energy regions, and processes in non-stationary systems, etc. It also helps to understand the influence of all these factors on structure of molecular spectra. In what follows we mainly consider the energy redistribution problems using as an example the predissociation of weakly-bound (van der Waals) complexes.

Intracavity Laser Spectroscopy (ICLS) is one of the most sensitive techniques of absorption spectroscopy. ICLS has a wide field of applications: molecular spectroscopy, spectroscopy of atmospheric gases and pollutions, investigation of kinetics chemical reactions and nonlinear optical phenomena such as stimulated Raman scattering, two-photon absorption, etc. The sensitivity of ICLS is limited by nonlinear processes in laser active media. The investigations of these processes permit achieving of ICLS sensitivity up to 10^-11 cm^-1.

Absorption spectroscopy with tunable diode lasers (TDLAS) is increasingly being used to monitor atmospheric trace gases down to low ppb-levels (10^-9 volume mixing ratio). This optical technique fulfills the requirements for trace gas analysis for most of the smaller molecules in the atmosphere with resolved absorption lines. The use of lead salt diode lasers gives access to the mid infrared spectral region, where the most important atmospheric constituents have strong rotational vibrational absorption bands. The application of high frequency modulation (FM) schemes is a promising tool for further sensitivity and detection speed improvements. With this technique, the absorption of a narrow spectral feature is measured by detecting the heterodyne beat signal that occurs when the FM optical spectrum of the probe wave is distorted by the spectral feature of the target gas. In this paper the basic principles of the FM measurement technique are reviewed, experimental data are discussed and measurements of ambient air are presented.

In this paper we present recent spectroscopic analysis performed in our laboratory for some atmospheric trace gases (ozone, nitrogen dioxide and nitric acid) in the infrared and far- infrared spectral regions: the goal of this work was to obtain accurate line parameters in these spectral regions because the accuracy of remote sensing measurements of trace gases in the atmosphere is strongly dependent upon the quality of the line parameters (line positions, intensities and widths for example) used for the retrievals of the measurements.

To illustrate the application of the theory described in the accompanying paper, we present results to define radial functions for the potential energy, adiabatic and nonadiabatic vibrational and rotational effects of the diatomic molecules LiH and SiS, including thus both a hydride (for which the effects of partial failure of the Born-Oppenheimer approximation are more readily detectable) and a non-hydride. The problem of current insufficiency of experimental data to permit the general separation of all effects is discussed. Alternative treatments to reduce spectral data are discussed critically in order to assess the dependence of the derived molecular parameters on the nature of the model.

After deriving the effective Hamiltonian for the motion of the nuclei in the field of the electrons, including terms for the adiabatic and nonadiabatic effects arising from the imperfect following by the electrons of the nuclear vibrations and rotations, we use symbolic computation in the spirit of Dunham to obtain analytic relations for the term coefficients as functions of the parameters in the radial functions in the effective Hamiltonian. The resulting terms include explicitly the proper dependence on the atomic reduced mass and on the mass of individual nuclei so that the values of the parameters are entirely independent of the effects of nuclear mass, in the spirit of Mendeleyev. Applications of this formalism to HCl and other molecules for which abundant vibration-rotational spectra are available illustrate the orders of magnitudes of the various coefficients and the accuracy of the computational approach.

The possibility of precession around the axis with an intermediate moment of inertia is shown for a system consisting of a particle coupled with an asymmetric core. The model considered has relevance to one-electron molecular Rydberg states. The predicted phenomenon may be observed in the lowest level splitting of rotational multiplets.

The configuration degeneration in a vibration-rotational spectrum of a nonrigid molecule is performed using a concept of symmetry group chains of models inserted into each other. The models arise in analytic solution of the problem on stationary states of molecules employing the perturbation theory. An example of the nonrigid molecule NH₃ in the nondegenerate vibrational state is considered. It is shown that the configuration degeneration treatment depends essentially on the type of the transition between energetically equivalent equilibrium configuration of the molecule.

The unified quantitative description has worked out for experimental data of Te₂ term values, g factors, lifetimes for levels of BO_u⁺ and Al_u states, along with the relative intensities in BO_u⁺-Xl_g, BO_u⁺-Xl_g transitions. It has been found that Al_u state is basically a ³(Sigma) ₁-component of the B³(Sigma) _u^- state.

Activities on the experimental and theoretical studies of large-amplitude molecular motions during recent years are reviewed. The modern situation and some difficulties of the high resolution vibration-rotation spectroscopy are considered in the framework of the large- amplitude motions problem. The models and methods developed for dealing with the problem and the potential functions of molecules are discussed.

An approximated analytical expression connecting the statistical uncertainties in rotational- vibration molecular constants with variations of Franck-Condon type integrals (FCI) has been obtained by applying a first order perturbation theory to the Morse oscillator model. The FCI dependencies on a presence of rotational-vibration interaction and effect of isotopic substitution have also been found in explicit forms.

Detailed description of the cluster structure of rotational spectra based on the analysis of the Rotational Energy Surface (RES) was realized mainly by Harter and Patterson. This concept is very useful because the classical trajectories on RES are closely connected to quantum rotational spectrum. We wish to derive the quantum Hamiltonian from the RES constructed on the pure classical grounds. Here we limit ourselves with the consideration of the centrifugal interaction alone and isolated vibrational states.

Recent developments in high resolution spectroscopy of weakly-bound systems open the unique possibility to study unimolecular reactions at the state-to-state level. We present a brief account of the quantum calculation on the vibrational spectra and predissociation dynamics of the helium complex with Br₂(B³II_Ou) molecule.

Using symmetry arguments effective vibrational-rotational Hamiltonians for bending vibrational levels of C₂H₂ and C₂D₂ have been written up to the fourth order in the Amat-Nielsen ordering scheme. These Hamiltonians describe all bending energy levels of molecules in ground electronic state. Hamiltonian for C₂D₂ contains Darling- Dennison resonance interaction terms (2(omega) ₄ is congruent to 2(omega) ₅). The latter differs slightly from that used by T.R. Huet, M. Herman, and J.W.C. Johns. It contains additional terms. It has been shown that these effective Hamiltonian are ambiguous. The transformations to the reduced form have been suggested.

Inverse problem which is a fit of a sample of experimental data to a multiparameter model of effective Hamiltonian H or an effective moment of transition M is an essential part of data reduction in molecular spectroscopy. In the present paper we describe a flexible inverse problem solver called GIP (General Inverse Problem) which, firstly, may be applied to a sufficiently large number of molecules, and secondly, enables one to overcome the major difficulties and limitations and provides a scientist with a useful tool to make studies in molecular spectroscopy.

The Pade-technique, developed before, along with the RKR-method is used for describing the absorption frequencies and energy levels of diatomic molecules. The inner wall of the potential energy curve is extrapolated from the force field adjusted in the fitting of low-laying energy levels, and a long-range part of the potential energy curve near dissociation is recovered by application of the RKR-method. The latter uses the extrapolated values of the vibrational energy levels. The similar calculations have been made through the adjusted spectroscopic parameters obtained by a phenomenological Pade-approach. Ab initio energies of the H₂ molecule have been exploited to test the Pade-models.

Conditions of development of explosive resonance absorption of power radiation of technological CO₂ laser in atmosphere have been obtained. Time evolution of vibrational temperature of carbon dioxide and translational temperature of atmosphere in the cross-section of Gauss beam have been calculated. Mechanism of explosive absorption of CO₂ laser radiation by water vapor is discussed.

In this paper we consider the two methods of transformation of the Hamiltonian of poliatomic molecules to arbitrary molecular coordinates. In these coordinates the classical Hamilton function on their form is shown to differ from the quantum mechanical Hamiltonian on the term U ' (q) in accord with Watson's results. The correspondence rule (p yields -in(alpha) /(alpha) R) can be applied for the transformation of the classical Hamilton function only in the Cartesian coordinates to the Hamiltonian of quantum mechanics.

Using an original double modulation set-up of an IR difference frequency laser spectrometer and a hollow cathode discharge cell with methane, in addition to a double phase sensitive detection method, it has been possible to distinguish between (nu) ₃ band spectral lines of the CH₃ radical and the much stronger lines belonging to the C-H stretching bands of the precursor and other stable species (C₂H₄, C₂H₆) that appear in the discharge. The method has proved to be very sensitive to detect population variations versus temperature of very weak transitions from highly excited levels of CH₄ and other stable species. The temperature characterization of several neutral species involved in the hollow cathode discharge has been tested and remarkably low temperatures have been obtained.

High resolution stimulated Raman spectra of the Q branches in the regions of the (nu) ₁ and (nu) ₃ Raman active modes of ethane ¹²C₂H₆) have been recorded. A complete analysis of the (nu) ₃ region in terms of a vibrational torsional coupling has been achieved. For the (nu) ₁ region spectra at 300 K, 173 K (static) and 30 K (jet expansion) have been recorded. On the basis of the 30 K spectrum, a preliminary assignment of the strongly perturbed spectra is presented.

Pressure dependences of carbon dioxide absorption coefficients for several CO laser transitions from 1850 to 1920 cm^-1 are measured. A comparison with the calculations (HITRAN-91) has been made. The calculated data for the Q-branch (1880.994 cm^-1) of the (20²0)_I-01¹0 CO₂ band are 20% lower than the measured ones. In the P-branch (1932.472 cm^-1) of the (11¹0) -00 degree(s)0) CO₂ band experimental absorption coefficients appeared to be 10 - 20% lower than the theoretical ones. The intensity and the self-broadening coefficient are determined for the P46 line of the (11¹0)_II-00 degree(s)0 carbon dioxide band.

Results of complex investigating of the conditions of appearing and objective laws of exhibiting a structural spectrum of anthracene-vapor fluorescence are presented. The data show that the usage of the suggested procedure permits us to obtain such highly-resolved spectra (in heated vapors of aromatic compounds) as those in the case of deep cooling in matrices and molecular jets.

This paper reports the observation of the molecular fluorescence circularity under irradiation with linear polarized light. The phenomenon arises as a result of partial transformation from alignment of the ensemble of molecular angular momenta into orientation due to quadratic correction to Zeeman effect. Circularity rate up to 0.05 at magnetic field 0.4 T was registered in B³(Sigma) _u^- (1_u^- yields $X³(Sigma) _g^-(0_g⁺) fluorescence of ¹³⁰Te₂ molecules. Data fitting showed that the electronic part of g factor caused by 1_u^-~0_u⁺ interaction is equal to G+/- is congruent to <0uJa+/- 1u> + 1.0023< 0uS+/- 1u>equals 2.72.

An absorption spectra of H₂S have been recorded at 0.006 and 0.012 cm^-1 resolution in 2000 - 9000 cm^-1 spectral region using the Kitt Peak national observatory Fourier-Transform spectrometer. Two spectra of H₂S at 1.49 Torr and at 9.99 Torr have been measured using non-linear least squares fitting to obtain line positions, intensities and self- broadening widths. The spectra identification has been made and twelve new bands have been assigned. The vibrational constants have been fitted to all known band centers.

Investigation of an absorption spectrum of D-isotope species of water vapor (one of the main absorption components of the atmosphere) in the two regions: 9161 - 9300 cm^-1 and 10280 - 10770 cm^-1 was carried out using a F₂⁺:LiF color center and a Nd³⁺ glass intracavity laser (ICL) spectrometers with threshold sensitivity to absorption about 10^-8 cm^-1.

The HDO and D₂O spectra have been recorded at room temperature with a high resolution Fourier-Transform spectrometer and a multipass cell with an absorption path length of 240 meters. The resolution used was about 0.01 cm^-1, the relative uncertainty in line positions was approximately +/- 0.0002 cm^-1.

The b³II_u-A¹(Sigma) _u⁺ interaction in Na₂ as manifested by A¹(Sigma) _u⁺ state Lande factors was investigated. Lande factors g_A were measured from the dispersion shape Hanle signal in fluorescence excited by 632.8 nm He-Ne and 647.1 or 676.4 nm Kr⁺ laser lines. The partial contribution g_Ab due to weak A~b interaction was extracted from measured g-factors. The electronic part of the spin-orbit (SO) interaction matrix element H_so^e equals 5.86 +/- 0.20 cm^-1 was determined by deperturbation fitting of g_Ab values.

The aim of this work is to study IR spectra of phosphine solutions in liquid argon at 94 - 96 K within the range of 5700 - 500 cm^-1. Special attention has been paid to the spectra analysis in an insufficiently known area of combination modes and overtones, the determination of integral absorption coefficients of corresponding transitions, spectral windows as well as phosphine solubility in liquid argon, which according to our data makes 2 X 10^-3 mole fraction.

The present work is devoted to studies on vibrational spectra and vibrational band contours of the fundamental modes of krypton and xenon fluorides in liquid Kr and Xe (T equals 130 and 180 K, respectively), CH₃CN, CCl₄, (CH₃)₂SO, non-aqueous HF and BrF₅ solutions.

Fourier transform spectra of water vapor have been recorded in the range 2500 - 4500 cm^-1. This spectral range is important for accurate modeling of radiative transfer phenomena in the Earth's atmosphere and in other planetary atmospheres, and is frequently used for atmospheric remote sensing applications. The measurements were performed with the combination of a 4 m base length White-type multipass absorption cell and an FTIR Spectrometer, the Bruker IFS 120 HR.

Remote sensing techniques based on millimeter and submillimeter spectroscopy have been shown to be powerful tools for the observation and measurement of many species of importance to the ozone cycle in the upper atmosphere. This paper discusses laboratory techniques and theoretical methods for the development of the data base which has been used as a basis for the interpretation of many of these remote sensing experiments. Recent work on HNO₃, H₂O, and HOOH is used as specific examples in this talk.

Experimental observation of the vibrational-rotational structure of pentad-dyad and octad- pentad hot bands for methane under non-equilibrium conditions of supersonic jet has been presented in our previous paper. New source of supersonic jet has been developed to increase stagnation temperature, temperature of gas before expanding in supersonic nozzle, up to 1300 K. Spectra of pentad-dyad, octad-pentad and tetradecad-octad hot bands (125 lines) for 1260 - 1298 cm^-1 and population of appropriate energy levels have been measured under these new experimental conditions for methane's stagnation temperature 800 - 1300 K using a pulsed IR spectrometer based on tunable diode laser.

The carbon dioxide dissociation has been investigated both theoretically and experimentally in nonequilibrium plasma of the glow and microwave gas discharges. Vibrational and gas temperature values have been measured for molecules in plasma and the dissociation degree for the isotopes ¹²C¹⁶O₂ and ¹³C¹⁶O₂ after the exit of the gas from the reactor core has also been measured. CARS and absorption spectroscopy (with help of frequency tunable diode lasers) methods were used for the investigation.

In this work the resonance interferometry technique has been used to measure the concentration of electron-beam-produced metastable states Ne[3s³P₂] and Ne[3s³P₀]. The interferograms obtained from large-scale Michelson interferometer with visualization of fringe region have provided an opportunity to observe dynamics of metastable atoms in e-beam plasma with time resolution of 10 ns as soon as their spatial distribution.

In this work the ozone production by electron beam (2 kA, 200 keV, 40 ns) was studied. Ozone concentration was measured by light absorption on the wavelength 0.25 + 0.01 micrometers . Experimental dependencies were obtained for ozone concentration dynamics and effective time of inversion from oxygen atoms to ozone. A calculation is given for plasmachemical production of oxygen atoms and contribution of the most substantial reactions is estimated depending on oxygen partial pressure in the gas mixture.

During recent years we studied the dynamics of collisionless SF₆ and NH₃ molecules' excitation by TEA CO₂ laser radiation. The main purpose of this research was to explain why the molecules, which have no exact resonance with the CO₂ laser field, absorb one or several IR quanta. We made measurements in a free supersonic jet and in a cell. Exciting energy densities were among 10^-2 and 2.0 J cm^-2. The fraction of molecules excited from individual rotational levels was measured and its dependences on the CO₂ laser frequency and on the energy density were investigated. We present the comparison of the experimental data with theoretical calculations, and questions that still remain unclear are discussed.

The measurements of half-width and shift of H₂O absorption lines due to foreign gas pressure are interesting for studying the intermolecular interactions in gases as well as for application of spectroscopic data in atmospheric optics. The half-width and shift of H₂O isolated absorption line of (nu) ₁ + 3(nu) ₃ vibration-rotation band were measured in the H₂O-air and H₂O-H₂ mixtures at varying the temperature of gases from 290 to 400 K. The measurements have been carried out using the dual-channel photo-acoustic spectrometer with a frequency tunable ruby laser, providing the spectral resolution of 0.01 cm^-1.

A general method for the calculation of matrix elements of multipolar terms of spherical top molecules is presented. It uses the tensorial algebra techniques that have been developed for these types of molecules, and is particularly suitable for computer implementation. Multipolar transition moments calculated in the lowest vibrational states of ¹²CH₄, are given in graphical form showing their dependences with respect to the internal dynamics of the molecule. It is then shown how this type of calculation can be naturally inserted in semi classical line broadening and shifting calculations.

Experimental results on the collisional self-shift and self-broadening of the 6₄₃ - 5$50) rotational water line at 439 GHz are presented in the temperature range 250 - 390 K. The (To/T) exponent for the shift and broadening are: (alpha) equals 2.59(20) and (beta) equals 0.62(9), respectively. A method for the remote measurement of gas temperature, based on spectral collisional shift and broadening, is proposed.

This paper presents the results of the study of the evolution of the HF band shape of the B...HF (B equals HCN, CH₃CN, OC, CO₂, Xe, Ar) complexes with the gas density varying from dilute gas to liquid. The vibration-rotation spectra of HCN/HF/Xe, CH₃CN/HF/Xe, HF/CO, HF/CO, HF/Xe, HF/Ar gaseous mixtures were obtained at T equals 293 K in the 4200 - 3500 cm^-1 range with the resolution >= 0.1 cm. The densities of the gaseous solvents have been varied in range 0 - 300 (Ar, Xe, CO), and 0 - 70 amagat (CO₂).

The IR absorption band shapes of gases at high densities can be used as a tool in studies of the rotational relaxation evidences and line mixing effect calculations. Such studies were very successful in the case of CO₂-Ar. We have carried out such an investigation for the CO- N₂ mixtures spectra in the CO 2-0 band region.

The majority of studies of collision broadening in infrared spectra of molecular gases assumes that observed vibration-rotation bands can be treated as the sum of Lorentz lines. However, it is well known now that line mixing (line coupling) effects cause the deviations from this model picture. This work extends studies of line mixing in the overtone region to the fundamental (nu) ₂ CO₂ Q branch broadened by He gas. The case of (nu) ₂ CO₂ gives us the possibility to investigate Q branch shapes including the nearest wings due to a significant intensity of this band. Moreover, this band is not perturbed strongly by the Coriolis interactions, so it is convenient for theoretical studies.

The rotational lineshapes in the FIR absorption of hydrogen fluoride in compressed gaseous helium were studied in the spectral region of 30 to 360 cm^-1. The line asymmetry was observed, and this fact was treated as a manifestation of spectral line mixing. Using the semiclassical impact approach, the asymmetry coefficients of lines were calculated. The method was modernized by adiabatic factorization of the distribution function of collisional frequencies via definite angular momentum vector variations. The calculated asymmetry coefficients are consistent with the measured ones within the experimental inaccuracies. The measured widths and the estimated shifts were compared with the literature data.

The wave equation describing states of a quantum system, that drifts with a velocity V in Markovian's thermostat, is introduced in this paper. This equation is valid in dipole approximation of an external electromagnetic field. We consider a subsystem of levels, and the dynamics of changing their states.

Within the framework of the line wing theory the peculiarities of line shape behavior in the intermediate part appear as a result of specific construction of the profile transitional from the line center to the line wing. In this paper it is shown that the experimental data in this case are satisfactorily explained.

The method for calculation of impact relaxation parameters of the spectrum of collisionally mixed lines is described. The numerical results are obtained for the lines of some molecules of symmetric type. The comparisons with experimental data and the discussion of results are given.

The purpose of this work is to give the method for the calculation of spectral lines half-widths of tetrahedral molecules. We consider the A and E rotational species for methane. A theoretical formulation is presented within the framework of Anderson-Tsao-Curnutte theory.

The principal purpose of the present study is to obtain the approximate theoretical estimation of pressure-induced line shift coefficients in the (nu) ₄ band of CH₄. A theoretical formulation is presented within the framework of Anderson-Tsao-Curnutte theory for calculation of pressure-shifts of F-species spectral lines.

Some years ago a new approach was proposed to investigate polyatomic molecules' spectra, where spectra were treated as an ensemble of all spectral lines. Statistical parameters of the whole ensemble have to be measured in this approach giving averaged information about spectral lines' distribution function and relaxation matrix. The approach appears to be very powerful giving qualitative information even for spectra with strongly overlapping lines. A theoretical model was developed to give physical meaning for measured values. That's why new information was obtained for polyatomic molecule spectra that could not be investigated previously due to problems of experiment and treatment. Thus some new effects were observed, such as line mixing and resonance behavior of collisional broadening and shifts.

Calculations of the absorption coefficient in vibration-rotation bands of CO and N₂O at high gas pressures are presented in this paper. Calculated results are compared with experimental data.

An improved method free from any fitting parameters is proposed and the package of computer programs is elaborated for 3-D classical trajectory simulation of pressure broadened vibration-rotation absorption bands contours of linear molecules. The calculations were carried out for a CO₂-Ar system with ab initio potential. An excellent agreement of theoretical results with data of absorption measurements in 4.3 micrometers far wing of CO₂ is obtained. The test of different trajectory models for interparticle collisions is presented.

Various methods of one- and two-frequency optical sounding of the gas and aerosol components of the atmosphere based on the using of dependence of resonance absorption coefficient on energetic and temporal parameters of optical radiation are presented in the paper.

Aldehydes are of great importance for the atmospheric photochemical processes. The direct usage of fluorescent method in the polluted atmosphere enables us to measure the concentration only of the aldehydes products since their spectra are covered. The separation of aldehydes is possible if the method of photofragments of spectroscopy is used. The proposed approach is based on the different dependences of COH-radical photodissociation rates for various aldehydes on exciting wavelength. In order to find the dependences the calculations of the low excited electron states of formaldehyde, acetaldehyde, and the vibration structure of these molecules were made. Thus the obtained data were used for calculation of the dissociation rates.