Nonadiabatic effects in (1~2)<Superscript>1</Superscript>Π–X<Superscript>1</Superscript>Σ<Superscript>+</Superscript> rovibronic transitions of KRb molecules

Numerical simulation of the effect of intramolecular electrostatic interactions on redistribution of relative intensities in the vibrational structure of (1 ~ 2)¹Π–X¹Σ⁺ rotationally resolved transitions of the KRb molecule is performed within the precision nonadiabatic model of coupled vibrational channels. It is established that mutual perturbation of electronically excited states modifies in a nontrivial way a nodal structure of nonadiabatic wavefunction of the (1 ~ 2)¹Π complex, which is possible to use for rising efficiency of twostep laser synthesis and stabilization of ultracold ensembles of KRb molecules in the ground electronic state.     

Observation of ultracold ground-state heteronuclear molecules

We report the observation of translationally ultracold heteronuclear ground-state molecules in a two-species magneto-optical trap containing 39K and 85Rb atoms. The KRb molecules are produced via photoassociation and detected by multiphoton ionization. We had characterized their temperature and measured their formation rate constant. We believe that the two-species trap could be used as a reliable source of ultracold molecules to be captured by electrostatic, magnetic, or optical traps. This possibility will certainly motivate further investigation of quantum collective effects as well as high-resolution spectroscopy of the rovibrational level structure of cold heteronuclear molecular systems.     

A review on the formation of heteronuclear cold molecules

In this paper, we review the present status of the formation of cold ground-state heteronuclear molecules in cold-trapped atomic samples. The experimental techniques and results are presented and reviewed. The molecule production rates are compared among themselves as well as with existing theories. We conclude that theoretical and experimental improvements are necessary to help plan new experiments. The experimental results indicate that KRb and RbCs are the best systems for heteronuclear molecule production.     

Photoassociative formation of ultracold polar KRb molecules

We investigate the effectiveness of creating polar ground-state KRb molecules by two-color photoassociative spectroscopy. In this process the molecules are formed from ultra-cold samples of K and Rb. Focusing on spin-polarized atoms we show that an effective pathway exists. In addition, we investigate the stability of the polar molecules in the presence of a thermal black-body radiation field.Received: 11 June 2004, Published online: 19 October 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 34.20.Cf Interatomic potentials and forces - 33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors - 34.50.-s Scattering of atoms and molecules     

Prospects for making polar molecules with microwave fields

We propose a mechanism to produce ultracold polar molecules with microwave fields. It converts trapped ultracold atoms into vibrationally excited molecules by a single microwave transition and entirely depends on the existence of a permanent dipole moment in the molecules. As opposed to production of molecules by photoassociation or magnetic-field Feshbach resonances, our method does not rely on properties of excited states or existence of Feshbach resonances. We determine conditions for optimal creation of polar molecules in vibrationally excited states of the ground-state potential by changing frequency and intensity of the microwave field. We also explore the possibility to produce vibrationally cold molecules by combining the microwave field with an optical Raman transition or by applying a microwave field to Feshbach molecules. The production mechanism is illustrated for KRb and RbCs.     

The photoassociative spectroscopy, photoassociative molecule formation, and trapping of ultracold \mathsf{^{39}K^{85}Rb}

We have observed the photoassociative spectra of colliding ultracold ³⁹K and ⁸⁵Rb atoms to produce KRb* in all eight bound electronic states correlating with the ³⁹K (4s) + ⁸⁵Rb(5p _1/2 and 5p _3/2) asymptotes. These electronically excited KRb* ultracold molecules are detected after their radiative decay to the metastable triplet (a state and (in some cases) the singlet (X ground state. The triplet (a ultracold molecules are detected by two-photon ionization at 602.5 nm to form KRb ⁺ , followed by time-of-flight mass spectroscopy. We are able to assign a majority of the spectrum to three states (2(0 ⁺ ), 2(0^-), 2(1)) in a lower triad of states with similar C ₆ values correlating to the K(4s) + Rb (5p _1/2) asymptote; and to five states in an upper triad of three states (3(0 ⁺ ), 3(0^-), 3(1)) and a dyad of two states (4(1), 1(2)), with one set of similar C ₆ values within the upper triad and a different set of similar C ₆ values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. [J. Chem. Phys. 111, 8857 (1999)], identifying three of our levels as v = 61, 62 and 63 of the 1 4(1) state they observed. We also argue that ultracold photoassociation to levels between the K(4s) + Rb (5p _3/2) and K(4s) + Rb (5p _1/2) asymptotes may be weakly or strongly predissociated and therefore difficult to observe by ionization of a (or X molecules; we do know from Kasahara et al. that levels of the 1 4(1) and 2 5(1) states in the intra-asymptote region are predissociated. A small fraction ( 1/3) of the triplet (a ultracold molecules formed are trapped in the weak magnetic field of our magneto-optical trap (MOT).Received: 22 September 2004, Published online: 23 November 2004PACS: 33.20.Fb Raman and Rayleigh spectra (including optical scattering) - 34.20.Cf Interatomic potentials and forces - 33.80.Ps Optical cooling of molecules; trapping     

Theoretical Study of the Electronic Structure of the KRb Molecule

Upon request of experimentalists now engaged in high-resolution spectroscopic investigations of the molecule KRb, we have determined the potential energy of electronic states (2S+1)Lambda((+)) correlating up to the limit K(5p) + Rb(5s) and of electronic states Omega((+/-)) correlating up to the limit K(4s) + Rb(4d(2)D(3/2)) in a large range of internuclear distance R. For the five states so far observed, the agreement between calculated and experimental molecular constants is good with DeltaR(e) < 0.08 ?, Deltaomega(e) < 6 cm(-1), and DeltaT(e) < 140 cm(-1). Extensive numerical data for energies versus R have been listed in a data base available at http://www.idealibrary.com. Copyright 2000 Academic Press.     

The KRb (2)(3)Sigma(+) Electronic State

High-resolution spectra of the (3)(1)Pi --> (2)(3)Sigma(+) system of the KRb molecule, obtained after excitation with fixed frequencies Ar(+) laser lines, were recorded on a Connes-type Fourier transform interferometer. Molecular constants of the first 14 vibrational levels of the (2)(3)Sigma(+) state are determined. The RKR potential energy curve is derived. The main spectroscopic constants for this triplet electronic state of the (39)K (85)Rb isotopic species are T(e) = 13 507.146(2) cm(-1), omega(e) = 48.6385(6) cm(-1), B(e) = 0.0254152(5) cm(-1), gamma = 0.00164(4) cm(-1), epsilon = -0.469(2) cm(-1), R(e) = 4.98345 ?, 𝒟(e) = 3447 cm(-1). Copyright 2000 Academic Press.     

Studies on heteronuclear diatomic molecular dissociation energies using algebraic energy method

The algebraic energy method (AEM) is applied to the study of molecular dissociation energy $D_e$ for 11 heteronuclear diatomic electronic states: $a^3\Sigma^+$ state of NaK, $X^2\Sigma^+$ state of XeBr, $X^2\Sigma^+$ state of HgI, $X^1\Sigma^+$ state of LiH, $A^3\Pi(1)$ state of ICl, $X^1\Sigma^+$ state of CsH, $A(^3\Pi_1)$ and $B0^+(^3\Pi)$ states of ClF, $2^1\Pi$ state of KRb, $X^1\Sigma^+$ state of CO, and $c^3\Sigma^+$ state of NaK molecule. The results show that the values of $D_e$ computed by using the AEM are satisfactorily accurate compared with experimental ones. The AEM can serve as an economic and useful tool to generate a reliable $D_e$ within an allowed experimental error for the electronic states whose molecular dissociation energies are unavailable from the existing literature.     

Isotopomer selective optimization of <Superscript>39</Superscript>K<Superscript>85</Superscript>Rb<Superscript>+</Superscript> and <Superscript>41</Superscript>K<Superscript>87</Superscript>Rb<Superscript>+</Superscript> using optimal control

We report on isotope selective three-photon ionization of two isotopomers of KRb by applying evolution strategies. The particularity of this experiment is based on the high resolution phase and amplitude modulation of the fs-laser pulses provided by a 2 × 640 pixel pulse shaper. The optimization in a closed feedback loop performed with spectrally broad pulses centered at 840 nm shows high enhancements of one isotopomer at the expense of the other isotopomer and vice versa. From the optimal laser field we aim to gain details about the selective ionization sequence and the wavepacket evolution on the involved vibrational states.     

Efficient production of ground-state potassium molecules at sub-mK temperatures by two-step photoassociation

We have developed a two-step " R-transfer" method that efficiently produces translationally ultracold potassium molecules in the X (1)Sigma(+)(g) electronic ground state. Laser-cooled atoms are initially photoassociated at large internuclear separation R to form molecules in high vibrational levels of the 1 (1)Pi(g) state, which are in turn excited by an additional laser to shorter-range Rydberg states such as 5 (1)Pi(u) and 6 (1)Pi(u). Subsequent radiative decay produces ground-state molecules at rates up to 10(5) molecules/second per vibrational level.     

Critical Evaluation of the Prediction of the Dissociation Energy and the Energy Spectrum of the Ground State of KRb by the Reduced Potential Curve Method

The estimates of the value of the dissociation energy and the energy spectrum of the KRb molecule made previously (O. Bludsky, M. Ju&rbreve;ek, V. Spirko, B. A. Brandt, and F. Jen&cbreve;, 1995, J. Mol. Spectrosc. 169, 555-582) are compared with the new experimental data (C. Amiot and J. Vergès, 2000, J. Chem. Phys. 112, 7068-7074) and the efficacy of the reduced potential curve (RPC) method is demonstrated. Copyright 2001 Academic Press.     

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     

Conversion of an atomic Fermi gas to a long-lived molecular Bose gas

We have converted an ultracold Fermi gas of 6Li atoms into an ultracold gas of 6Li2 molecules by adiabatic passage through a Feshbach resonance. Approximately 1.5 x 10(5) molecules in the least-bound, v=38, vibrational level of the X1Sigma(+)(g) singlet state are produced with an efficiency of 50%. The molecules remain confined in an optical trap for times of up to 1 s before we dissociate them by a reverse adiabatic sweep.     

Vibration of small molecules on Pt(1 1 1) surface

The adsorption of methanol and other small molecules onto transition metal surfaces is an important issue in electrochemistry, fuel cells, etc. Despite the overwhelming interest there are still unresolved issues beginning from the geometry of the adsorbed species to the correct assignments of different vibrational modes of the adsorbed molecules on the surface.In order to understand the adsorption processes, we have performed density functional theory (DFT) calculations for small molecules (methanol, formaldehyde, formic acid) on Pt(1 1 1) surfaces. We investigated the nature of the metal-ligand bonding in these adsorption processes using electron density difference and PDOS (partial density of states) methods. Ab initio vibration spectra have been calculated for these systems.     

Association of riboflavin,caffeine, and sodium salicylate in aqueous solution

We have used UV and visible spectrophotometry to study self-association of aromatic riboflavin molecules (RFN, vitamin B₂, 7,8-dimethyl-10-N-(1′-D-ribityl)isoalloxazine) in aqueous solution (pH 6.86) at T = 298 K, using a dimer model. We have determined the equilibrium dimerization constant for riboflavin, K_dB = 125 ± 40 M⁻¹. We have studied heteroassociation in the system of molecules of 7,8-dimethyl-10-ribitylisoalloxazine with 1,3,7-trimethylxanthine (caffeine) and sodium salicylate (NAS) in aqueous solution (pH 6.86; T = 298 K). We have determined the heteroassociation constants for RFN-NAS and RFN-caffeine molecules in the absence and in the presence of urea in solutions using a modified Benesi-Hildebrand equation: 25 ± 4, 17 ± 3, and 74 ± 11, 53 ± 7 M⁻¹ respectively. We have determined the dimerization constants for NAS (2.7 ± 0.5 M⁻¹) and caffeine (17.0 ± 1.5 M⁻¹). We conclude that heteroassociation of the aromatic molecules leads to a lower effective riboflavin concentration in solution, and the presence of urea in mixed solutions leads to an decrease in the complexation constants for the RFN-NAS and RFN-caffeine systems. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 188–194, March–April, 2007.     

Theoretical study of slowing supersonic CH3F molecular beams using electrostatic Stark decelerator

We have calculated the Stark effect of CH3F molecules in external electrical fields,the rotational population of supersonic CH3F molecules in different quantum states,and analyse the motion of weak-field-seeking CH3F molecules in a state |J = 1,KM = 1 inside the electrical field of a Stark decelerator by using a simple analytical model.Threedimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator,and the results are compared with those obtained from the analytical model,including the phase stability,slowing efficiency as well as the translational temperature of the slowed molecular packet.Our study shows that with a modest dipole moment(～1.85 Debye) and a relatively slight molecular weight(～34.03),CH3F molecules in a state |J = 1,KM = 1 are a good candidate for slowing with electrostatic field.With high voltages of ±10 kV applied on the decelerator,molecules of 370 m/s can be brought to a standstill within 200 slowing stages.     

Nonlinear optical properties of stilbene and azobenzene derivatives containing azaphosphane groups

We have studied the nonlinear optical (NLO) properties of some donor–acceptor molecules with stilbene and azobenzene molecules as backbone. We have used the nitro group as the acceptor and azaphosphane (R₃P=N–) as the donor group. To study the effect of variation of NLO properties, we have replaced the substituents (Rs) connected to the phosphorus atom by methyl, amine and phenyl groups. We find that both first-order polarizability and hyperpolarizabilities are larger for stilbene derivatives and is maximum for the phenyl substitution. Second-order polarizability is higher for methyl substitution. We have also obtained the two-photon absorption cross-section for these molecules. We find that both one-photon and two-photon absorption cross-sections are maximum for the same excited state (first excited state in the case of stilbene and second excited state in the case of azobenzene derivatives).     

Quantum ergodicity and energy flow in molecules

We review a theory for coupled many-nonlinear oscillator systems that describes quantum ergodicity and energy flow in molecules. The theory exploits the isomorphism between quantum energy flow in Fock space, that is, vibrational state space, and single-particle quantum transport in disordered solid-state systems. The quantum ergodicity transition in molecules is thereby analogous to the Anderson transition in disordered solids. The theory reviewed here, local random matrix theory (LRMT), describes the nature of the quantum ergodicity transition, statistical properties of vibrational eigenstates, and quantum energy flow through the vibrational states of molecules. Predictions of LRMT have been observed in computational studies of coupled nonlinear oscillator systems, which are summarized here. We also review applications of LRMT to molecular spectroscopy and chemical reaction rate theory, including adoption of LRMT in theories that predict rates of conformational change of molecules taking place at energies corresponding to those below and above the quantum ergodicity transition. A number of specific examples are reviewed, including the application of LRMT to predict (1) dilution factors of IR spectra of organic molecules, (2) rates of conformational change in chemical and photochemical reactions, (3) conformational dynamics of biological molecules in molecular beams, (4) rates of hydrogen bond breaking and rearrangement in clusters of biological molecules and water, and (5) excited state proton transfer reactions in proteins.     

Theoretical study of the phosphorescence of 8-azasteroids

We have used quantum chemical methods for a theoretical study of the luminescent characteristics (including estimating the rate constants for intramolecular T₁ → S₀ electronic transitions) of the molecules of four immunoactive compounds of the 8-azasteroid class. We have established that the T₁ state is localized on the enaminodicarbonyl moiety that is common to all the molecules. We have shown that for the studied compounds, the phosphorescence spectra and the physical mechanisms for deactivation of the lower triplet state T₁ are similar. For all the compounds, the results of the theoretical study are consistent with the corresponding conclusions of experimental studies of 8-azasteroids. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 751–755, November–December, 2006.