Predissociation resonances in CO and IBr. Smooth exterior scaling combined with the discrete variable representation

Smooth exterior scaling (SES) and the discrete variable representation (DVR) are combined to accurately compute predissociation resonances of a bound state non-adiabatically coupled to a dissociative state. For the CO( predissociation interaction good agreement is found with approaches based on optical potentials and complex scaling. The comparison is done both in the diabatic and the adiabatic representation. The effect of the coupling strength in the IBr predissociation interaction and the transition from the diabatic to the adiabatic picture was studied by computing resonances for coupling strengths from up to . The transition from weak (diabatic) to strong (adiabatic) coupling was clearly seen. The intermediate case leads to a complicated resonance distribution. Comparison was made with recent studies using pump-probe spectroscopy [M. Shapiro, M.J.J. Vrakking, A. Stolow, J. Chem. Phys. 110, 2465 (1999)]. It was found that the overall features of the experiment could be explained from the resonance distribution, but for a detailed comparison more accurate potential energy surfaces and couplings are needed. Received 12 July 1999 and Received in final form 6 December 1999     

Cesium satellite band at 875.2 nm stemming from the Cs 2 0 g + (6 p 2 P 1/2 +6 s 2 S 1/2 ) state

We measured a very distinct satellite band at 875.2 nm between two resonance lines of cesium. Spectral simulation using Spies and Meyer [#!ref1!#] ab initio potential curves and an appropriate transition dipole moment function was compared with experimental profile. Implications of the investigated satellite band at 875.2 nm in the field of ultracold cesium atom collisions are discussed with a special emphasize to new possibilities of the photoassociation of two ground state atoms leading to the formation of ultracold intermediate long-range molecules. Received 07 March 2001 and Received in final form 14 May 2001     

Blue satellite bands of KRb molecule: Intermediate long-range states

Three distinct satellite bands at 730-736 nm and a single shoulder at 755.5 nm that we assigned to KRb heteronuclear molecule are found in absorption measurements of hot K + Rb vapor. The interpretation of these bands is discussed in terms of recent ab initio calculations of the relevant potential curves. Semiclassical spectral simulations were performed with ab initio potentials and approximate transition dipole moment functions showing a good agreement with observations. The probabilities of cold molecule photoassociative formation into the external well of the double minimum (5)0⁺ state and decay to the ground state are discussed, and relative yields of molecular formation were estimated by using quantum mechanical calculations. Received 15 October 2001     

Vibrational resonances of non-rotating HCN in the excited electronic state

A multi reference internally contracted configuration interaction (MRCI) method is used to generate the potential energy function (PEF) of the excited electronic state of HCN molecule. The analytic representation of the PEF is employed to calculate complex eigenvalues (resonance positions and widths) by a discrete variable representation (DVR) of the Hamiltonian for the non-rotating (J =0) molecule. The computational method used is a variant of the filter-diagonalization technique based on a recursive polynomial expansion of the absorbing-boundary-conditions (ABC) Green operator. Reasonable agreement with existing experimental data is found. Received 27 July 1999 and Received in final form 18 October 1999     

Nonadiabatic fragmentation of excited molecular ions: An exploratory study for

The photodissociation of was studied in a one-dimensional approximation, with the aim of understanding the nonadiabatic features of the fragmentation dynamics. In the collinear arrangement of the system, the three lowest excited surfaces (states) interact via two avoided crossings outside the Franck-Condon region, and they are strongly coupled radially by nonadiabatic terms. Electronic transition probabilities for the process , with in one of the three lowest electronic states involved in the fragmentation, were calculated using the semiclassical multichannel S-matrix within the half-collision approach to photodissociation. The reliability of the semiclassical theory, for treating multichannel nonadiabatic processes was analyzed, and inelastic cross-sections for the three processes of electronically selected fragmentations were calculated. The structure found in the calculated absorption lineshapes reveals the marked influence of the nonadiabatic couplings between excited states in the fragmentation dynamics of this molecular ion. Received: 6 March 1998 / Revised: 7 March 1998 and 17 June 1998 / Accepted: 23 June 1998     

High-resolution measurements of line intensity, broadening and shift of CO around m

Fundamental spectroscopical parameters of CO₂ are reported using a high resolution, direct absorption spectrometer, based on a distributed feed-back diode laser emitting at 2 μm. Line intensity, self- and foreign broadening and shift, with N₂ and O₂ as foreign gases, have been measured with high accuracy in the combination band of CO₂, for 13 lines of the R branch, from R(22) up to R(46). Comparison with available data is made, when possible, and a generally good agreement has been found. Received: 24 April 1998 / Received in final form: 28 October 1998     

Splitting of vibrational mode of CO isotopic species in the unstable trapping site in argon matrix

FTIR spectra of the antisymmetric stretch and symmetric bending vibrational modes of isotopic species of CO₂ trapped in argon matrix are recorded at 5 K with a resolution of . A splitting of the mode is observed for the different species in the trapping site termed unstable. Considering this splitting and the width of the line observed for this unstable site, one expects this site to be larger than the stable one. A theoretical model is elaborated to interpret this splitting. Calculations performed at harmonic level of approximation for vibrational modes in a single substitutional site (S1) and a double substitutional one (S2) in a fcc distorted argon lattice to minimize the free energy of the molecule-matrix system, show the splitting to occur in the larger site. The latter result leads us to invert former attribution of the sites: the stable site is a single substitutional one, whereas the unstable site is a double substitutional one. Received: 27 January 1998 / Revised: 30 July 1998 / Accepted: 17 August 1998     

Self- and foreign-broadening and shift coefficients for C2H2 lines at 1.54 μm

In this article we present experimental data for line parameters measurements of several transition lines of overtone bands of C₂H₂ at 1540 nm. The measurements were done with a spectrometer based on a semiconductor diode laser and a direct absorption spectroscopy scheme. Broadening and shift coefficients have been measured for the pure gas or in mixtures with N₂, O₂ and CO₂ as perturbing gas. Received 6 November 2000 and Received in final form 13 March 2001     

Diode laser spectroscopic measurement and impact theoretical analysis of collision broadening of acetylene band transitions

A near infrared diode laser spectrometer has been used for measurement of line shapes of the rotational transitions of the () overtone-combination band of acetylene perturbed by oxygen and air. Pressure-broadening coefficients and line strength parameters are extracted from least squares fitting of the spectra with Voigt profiles. A detailed calculation of pressure-broadening coefficients for the self, nitrogen and oxygen broadening cases has been performed by using semi-classical impact theory based on quadrupolar and dispersion interactions. The relative importance of the intermolecular interactions has been investigated and it is found that for these weak interaction cases dispersive terms have a dominant role in line broadening. This is more pronounced for the O₂-broadening case. We have included all the non-resonant terms till convergence is achieved. The cutoff parameter b₀ of the Anderson procedure has been determined separately for each non-resonant process. In order to include the orientation effect of the molecules at the moment of collision we have considered an average kinetic collision diameter which sets the lower limit of b₀. This improves the result considerably and the calculated values are close to the observed results. The J-dependence of the half width is also reported and shows decrease for large J-values. Received 24 November 1999     

High resolution polarization spectroscopy and laser induced fluorescence of CO<Subscript>2</Subscript> around 2μm

High resolution Infrared Polarisation Spectroscopy (IRPS) and Infrared Laser Induced Fluorescence (IRLIF) techniques were used to probe CO₂/N₂ binary gas mixture at atmospheric pressure and ambient temperature. The probed CO₂ molecules were prepared by laser excitation to an overtone and combination ro-vibrational state (12⁰1, J=15) of CO₂, centred at 4988.6612 cm^-1. IRPS and IRLIF line profiles were recorded for several CO₂/N₂ binary mixtures. The observed IRLIF line shapes have the expected Lorentzian form while the observed IRPS line shapes are narrower by a factor of two than those recorded with the IRLIF and appear to have a Lorentzian-cubed profile. The recorded line profiles provide measurements of the pressure-broadening coefficient directly at atmospheric pressure. The Full-Width-Half-Maxima (FWHM) pressure broadening coefficients are measured, based on IRLIF, to be 0.2174±0.0092 cm^-1atm^-1 and 0.1327 ±0.0077 cm^-1atm^-1 for self- and N₂ collision broadening, respectively. The broadening coefficients obtained based on IRPS were measured to be ~8% larger than those obtained with IRLIF.     

Temperature dependence of self-broadening in molecular-oxygen spectrum

Summary The ^p P(k=9) magnetic-dipole transition of the oxygen 0-0 vibrational band of the red systemb ¹Σ _g ⁺ ←X ³Σ _g ⁻ was observed with absorption spectroscopy using a tunable CW diode laser. A systematic investigation of the self-collisional broadening was performed for different gas pressures and temperatures. The temperature dependence of the self-broadening coefficient was determined to beT ^{−(1.02±0.05)}. Our results are of interest for collisional theory and as reference data in atmospheric monitoring applications. The authors of this paper have agreed to not receive the proofs for correction.     

A multispectrum fitting procedure to deduce molecular line parameters: Application to the 3-0 band of 12 C 16 O

To deduce accurate infrared molecular line parameters (positions at zero pressure, pressure-shifting and pressure-broadening coefficients, collisional narrowing coefficients, and intensities) from rovibrational spectra, an automatic method based upon a multispectrum fitting procedure has been set up, able to treat simultaneously several laboratory Fourier transform spectra. A validation of this method, using absorption spectra of the 3-0 vibrational band of CO around 6 350 cm^-1, already used to measure line intensities and self-broadening coefficients, is presented, and the advantages of the method are pointed out. The self-collisional narrowing of CO was observed and determined for the first time in Fourier transform spectra: β = 0.028±0.004 cm^-1 atm^-1 at about 296 K. Received 21 September 2000 and Received in final form 15 January 2001     

Isotope dependent predissociation in the C 1 Σ + , v =0 and v =1 states of CO

Rotationally resolved spectral lines in the C - X (1, 0) band of carbon monoxide are investigated under high resolution using a coherent vacuum ultraviolet laser source, continuously tunable near 107 nm. Transition frequencies are determined by calibrating against a reference standard of iodine lines, recorded with saturation spectroscopy in the visible range, yielding an absolute accuracy of 0.003 cm^-1 in the vacuum ultraviolet. Improved molecular constants for the excited state are derived and no effects of perturbation are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime of the C ¹ Σ ⁺ , v = 1 state for five natural isotopomers of carbon monoxide: τ( ¹² C ¹⁷ O ) = 280 ps, τ( ¹² C ¹⁸ O ) = 210 ps, τ( ¹³ C ¹⁶ O ) = 295 ps, τ( ¹³ C ¹⁷ O ) = 160 ps, and τ( ¹³ C ¹⁸ O ) = 150 ps. Within the accuracy of the present measurements no effects of J-dependent lifetimes were observed, for neither of the isotopomers. In addition direct time domain measurements of the lifetime of the C ¹ Σ ⁺ , v = 0 and v = 1 states of the main isotopomer are performed in a pump-probe experiment using a picosecond VUV-laser, yielding τ( ¹² C ¹⁶ O ) = 1780 ps for v = 0 and τ( ¹² C ¹⁶ O ) = 625 ps for v = 1. For C ¹ Σ ⁺ , v = 0 in ¹²C¹⁶O and ¹³C¹⁶O the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous results showing pure radiative decay in this state; the error margins however do not exclude some low level of predissociation. The measurements indicate that the C ¹ Σ ⁺ , v = 0 state of the ¹³C¹⁸O isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for ¹²C¹⁶O.) From the combined data predissociation yields upon excitation of the C ¹ Σ ⁺ , v = 1 state are derived, lying in the range 0.84-0.91 for the five less abundant isotopomers; for the main ¹²C¹⁶O isotopomer a strongly deviating predissociation yield of 0.65 is deduced. Received 21 December 2000 and Received in final form 26 March 2001     

Theoretical analysis of Resonant Auger Electron Spectra produced by isolated resonances

Summary  Line profiles of Resonant Auger Electron Spectra produced by isolated resonances are analyzed by separating the contributions due to the direct, resonant and interference terms and taking explicitly into account the effects due to the finite bandwidth of the incident radiation. The mean kinetic energy of the emitted electron and the spectral width of the Auger lines are also studied as functions of the parameters characteristic of the incident radiation. The general expressions derived by the theory are applied to the analysis of the lineshapes produced by a specific electronic transition taken from the autoionization spectrum of the CO molecule.     

Photofragment space distribution in the photodissociation of NaI in the spectral range 315–370 nm: the role of molecular axis rotation

The first determination of translational anisotropy parameters β in the photodissociation of NaI molecules in the spectral range 315–370 nm is reported. The anisotropy parameters were determined by the analysis of Doppler resolved absorption profiles of Na(²S_1/2) atoms produced in the photodissociation of NaI by linearly polarized light. The profiles were recorded for two orientations of the photolysis light: parallel and perpendicular to the direction of the probe beam. The value of the parameter β was obtained from a simultaneous fit of the profiles. The role of the rotation of the parent molecules on the branching ratio between parallel and perpendicular transitions in NaI during dissociation is discussed.     

Optical potential discrete variable representation method in the adiabatic representation

The optical potential discrete variable representation method (OP-DVR) has been applied recently to calculate resonances in the framework of the diabatic representation [J. Chem. Phys. 101, 7580 (1994)]. This method is based on the conjoint use of the discrete variable representation (DVR) method and the properties of a complex absorbing potential (CAP). The OP-DVR method is the DVR version of the CAP stabilization method initially proposed by Jolicard and Austin [Chem. Phys. Lett. 121, 106 (1985)]. In the present study, we show that this efficient and accurate method can also be applied within the adiabatic representation since it allows one to overcome in a simple way, numerical difficulties associated with the first derivative operator which appears in the expression of non adiabatic couplings. Within the OP-DVR method, the choice of the representation (diabatic or adiabatic) is governed by physical arguments and by the fact that the potentials and the couplings are known in one or the other of these two representations. In the case where the potentials and the couplings are obtained in the adiabatic representation, we show in this paper that the transformation into the diabatic framework is not necessary. We demonstrate that the discrete variable representation can be a simple and an efficient way to deal with the adiabatic representation. Received: 30 April 1998 / Revised: 29 September 1998 /Accepted: 21 October 1998     

N2- and O2-broadening coefficients in the ν2 and ν5 bands of CH3F at 183 and 298 K

The N₂- and O₂-broadening coefficients of 33 rovibrational lines in the ν₂ and ν₅ bands of ¹²CH₃F were measured at 183 K using a diode-laser spectrometer. The measurement of these coefficients was also realized at room temperature for 10 of these lines to determine their temperature dependence. The line parameters were obtained by fitting to the experimental profile the Voigt lineshape, and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the pressure-broadening coefficients were also performed for the same temperatures from a semiclassical model involving electrostatic, induction and dispersion interactions in the intermolecular potential. The calculated values reproduce well the experimental data for both temperatures and both perturbers and the theoretical temperature dependence of the broadening coefficients is in satisfactory agreement with that derived from the measurements.     

Frequency measurements in the b <Superscript>3</Superscript>Π(0<Subscript>u</Subscript><Superscript>+</Superscript>) - X <Superscript>1</Superscript>Σ<Subscript>g</Subscript><Superscript>+</Superscript> system of K<Subscript>2</Subscript>

Absolute transition frequencies of the b ³Π(0_u ⁺) - X ¹Σ_g ⁺ system of K₂ were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K₂ molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K₂ molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined.     

Photoionization and detection of ultracold Cs<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> molecules through diffuse bands

We present the results of absorption measurements in a cesium vapor around 630 K, together with photoionization spectra through a resonance-enhanced two-photon absorption of ultracold cesium dimers created after photoassociation of ultracold cesium atoms. The maximum efficiency of the ultracold molecule ionization is found for wavelengths where absorption at thermal energies is the strongest, in agreement with our theoretical simulations of both processes, involving the so-called Cs₂ diffuse bands. This result will be helpful for further optimization of such a direct way of detection of ultracold molecules. Received 13 September 2001     

Orientation of Cs 6p 2P3/2 atomic photofragments in a magnetic field: interference in the photodissociation of diatomic molecules

In a magnetic field, Cs₂ molecules were excited from the ground X¹Σ⁺_g(v_X=0,J_X=55) level to the D ¹Σ⁺_u(v=46,J=54) level by dissociation laser light linearly polarized parallel to the field, for which the magnetic sublevels were degenerated and thus all the transitions between them were simultaneously stimulated. Probe laser light excited the dissociated Cs 6p²P_3/2 atomic fragments to 6p²D_3/2 level and the resultant 6p²P_1/2 - 6d²D_3/2 emission was detected as the function of the wavelength of the probe light. The populations of the 6p²P_3/2,mj magnetic sublevels were determined from the relative strengths of the 6p²P_3/2,mj - 6d²D_3/2,m'j transitions induced by the probe light. Non-zero orientation O₀ was found in the ensemble of dissociated Cs 6p²P_3/2 atomic fragments. The orientation O₀ increased as the magnetic field strength increased. It was demonstrated both experimentally and theoretically that the orientation O₀ was induced through the interference in the excitation and dissociation paths in the presence of an external magnetic field, even when all degenerated transitions between the magnetic sublevels of the molecules are simultaneously excited by the light linearly polarized parallel to the field.