Stark quantum beat spectroscopy of polyatomic molecules

We derive analytical expressions for Stark quantum beat signals of polyatomic molecules and discuss them with regard to molecular and geometrical parameters. The general treatment is specified for near prolate asymmetric rotor molecules and a method for determining rotational constants and all components of the dipole moment of electronically excited polyatomic molecules is presented. The method is tested and illustrated for the vibrationlessS ₁ state of deuterated propynal (HC ≡ CCDO,C _s symmetry) and its lowest frequency non-totally symmetric state 12¹. The results of the vibrationless state are compared with structural data reported in the literature. For the 12¹ state we obtainA=1.5004(43) cm^?1,B=0.16131(34) cm^?1,C=0.14623(34) cm^?1, and the components of the electric dipole moment in the molecular plane μ _a =?0.88(2)D, μ _b =1.03(2)D. Furthermore, it is shown that the modulation depth of Stark quantum beat signals can be utilized to quantify the contribution of the individual components of the transition moment to the total emission.     

Determination of asymmetry splittings in the polyatomic molecule propynal by Stark quantum beat spectroscopy

Coherences among asymmetry-split rotational levels in a molecule can be created when a weak electric field is applied. The quantum beats superimposed on the time-resolved fluorescence decay are utilized for the accurate measurement of asymmetry splittings. The technique is exemplified for selected vibronicS ₁ states of propynal and αD-propynal and the results are compared with conventional (i.e. frequency domain) spectroscopic data. The applicability of the presented method of coherence spectroscopy is discussed.     

Stark coefficients for highly excited rovibrational states of H2O

Quantum beat spectroscopy is combined with triple-resonance vibrational overtone excitation to measure the Stark coefficients (SCs) of the water molecule for 28 rovibrational levels lying from 27,600 to 41,000 cm(-1). These data provide a stringent test for assessing the accuracy of the available potential energy surfaces (PESs) and dipole moment surfaces (DMSs) of this benchmark molecule in this energy region, which is inaccessible by direct absorption. SCs, calculated using the combination of a high accuracy, spectroscopically determined PES and a recent ab initio DMS, are within the 1% accuracy of available experimental data for levels below 25,000 cm(-1), and within 4.5% for coefficients associated with levels up to 35,000 cm(-1). However, the error in the computed coefficients is over 60% for the very high rovibrational states lying just below the lowest dissociation threshold, due, it seems, to lack of a high accuracy PES in this region. The comparative analysis suggests further steps, which may bring the theoretical predictions closer to the experimental accuracy.     

Calculation of avoided crossings for highly excited Stark states of Rb

Using the method of diagonalization, in which zero-field wavefunctions from a potential model are chosen as a basis, we calculate positions and widths of anticrossings for highly excited Stark states of Rb with principal quantum number n up to 49. We obtain the theoretical positions and widths in good agreement with available experimental values, and we present scaling laws of the field positions and widths of anticrossings that can be used to provide information for future experiments.     

Accidental vibrational degeneracy in vibrational excited states observed with ultrafast two-dimensional IR vibrational echo spectroscopy

The coupling between the OD stretch v=2 level and benzene-ring modes in 2-methoxyphenol-OD (hydroxyl H replaced by D) is observed with ultrafast two-dimensional (2D) IR vibrational echo spectroscopy. Because of this coupling, the 1-2 transition peak in the 2D spectrum is split into a doublet with peaks of approximately equal amplitudes. Several molecules and solvents were used to study this phenomenon. Near-IR (NIR) spectroscopy measurements and density-functional theory calculations (B3LYP6-31+G(d,p) level) were also applied. Experimental results and calculations show that the OD stretch 1-2 transition is coupled to a combination band related to the benzene-ring motions. A simple quantum-mechanical model indicates that the combination band has a frequency of 5172 and 5176.5 cm(-1) in CCl4 and hexane, respectively. The transition between this combination band and the ground state is too weak to detect by NIR. The transition between this band and the OD stretch first excited state is also so weak that most of the intensity of the doublet comes from the oscillator strength produced by coupling to the OD stretch. The model gives the coupling strengths as 6.5 and 7 cm(-1) in CCl4 and hexane, respectively.     

Calculation of highly excited vibrational states using a Richardson-Leja-Davidson scheme

An efficient computational scheme for calculating highly excited vibrational eigenstates is proposed, combining a Richardson-Leja spectral filter with a novel version of the Davidson method [J. Comput. Phys. 17, 87 (1975)]. Highly excited eigenstates of the Rb2 and H2O molecules are computed to test and verify the method. On the average less than 2.5 outer recursions per eigenstate are needed. For each outer Davidson recursion, less than 20 inner filter recursions per eigenstate are needed on the average.     

Second-derivative method: Application to vibrational spectroscopy in excited electronic states

The second-derivative method, which has been known to be useful for finding peaks overlapped in a broad band, is applied to u.v. and visible absorption bands to derive vibrational frequencies in excited electronic states of molecules in solution. By using this method, much better estimates of vibrational frequencies are possible for Franck—Condon active modes than can be made from the absorption spectrum itself. Computational procedure and the results obtained for trans-1,3,5-hexatriene, azulene, pyrazine and anthracene are described with remarks about the effectiveness and limitations of the second-derivative method.     

Fluorescence from SF6 in highly excited vibrational states: An overview

The spectroscopy of SF₆, excited in its quasi-continuum by IR multiphoton absorption, has been recorded by IR fluorescence from ν = 700 to 1300 cm⁻¹ with a highly sensitive device. The far resonance fluorescence exhibits structures directly connected to the intramolecular couplings. A model of couplings has been developed, the parameters of which are fixed by the experimental results. The strongest couplings (orders k = 3 and 4) have a density so low that they produce only a perturbative redistribution of the ν₃ mode. The dissipative redistribution is produced by the highest orders k⩾5 and can be represented by a half-linewidth γ_d∼1.5 cm⁻¹ for E_vib∼ 15,000 cm⁻¹. The onset of the SF₆ quasi-continuum is also predicted by the model, with characteristics in full agreement with published data.     

Spectroscopy of highly excited vibrational states of HCN in its ground electronic state

An experimental technique based on a scheme of vibrationally mediated photodissociation has been developed and applied to the spectroscopic study of highly excited vibrational states in HCN, with energies between 29,000 and 30,000 cm(-1). The technique consists of four sequential steps: in the first one, a high power laser is used to vibrationally excite the sample to an intermediate state, typically (0,0,4), the nu3 mode being approximately equivalent to the C-H stretching vibration. Then a second laser is used to search for transitions between this intermediate state and highly vibrationally excited states. When one of these transitions is found, HCN molecules are transferred to a highly excited vibrational state. Third, a ultraviolet laser photodissociates the highly excited molecules to produce H and CN radicals in its A 2Pi electronic state. Finally, a fourth laser (probe) detects the presence of the CN(A) photofragments by means of an A-->B-->X laser induced fluorescence scheme. The spectra obtained with this technique, consisting of several rotationally resolved vibrational bands, have been analyzed. The positions and rotational parameters of the states observed are presented and compared with the results of a state-of-the-art variational calculation.     

Quantum chemistry and spectroscopy of highly excited states of coordination compounds

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Institute of Chemistry and Chemical Technology, Siberian Branch, Academy of Sciences of the USSR. Branch of the Institute of Chemical Physics, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 6, pp. 90–103, November–December, 1988.     

Dipole moments of triethyl(phenoxy) derivatives of Group IVB elements in ground and electronically excited states

Russian Chemical Bulletin - The dipole moments of the trialkyl(phenoxy) derivatives of the Group IVB elements in the ground and first singlet excited states show that in the excited state the...     

Theoretical investigation of highly excited vibrational states in DFCO: calculation of the out-of-plane bending states and simulation of the intramolecular vibrational energy redistribution

A previously developed modified Davidson scheme [C. Iung and F. Ribeiro, J. Chem. Phys. 121, 174105 (2005)] is applied to compute and analyze highly excited (nu2,nu6) eigenstates in DFCO. The present paper is also devoted to the simulations of the intramolecular vibrational energy redistribution (IVR) initiated by an excitation of the out-of-plane bending vibration (nnu6, n=2,4,6, . . . ,18, and 20). The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. A comprehensive comparison with experimental data as well as with previous simulations of IVR in HFCO [G. Pasin et al. J. Chem. Phys. 124, 194304 (2006)] is presented.     

Ultrafast vibrational dynamics observed in higher electronic excited states of iodine using pump-UV DFWM spectroscopy

By using a combination of an initial pump pulse and a degenerate four-wave mixing process, we show that an interrogation of the vibrational dynamics occurring in different electronic states of molecules is possible. The technique is applied to iodine. The initial pump pulse is used to populate the B((3)Pi) state of molecular iodine in the gas phase. Now, by using an internal time delay in the DFWM process, which is resonant with the transition between the B state and a higher lying ion-pair state, the vibrational dynamics of the B state and the ion-pair state could be observed. States of even symmetry are investigated, which are accessed by a one photon transition from the B state. By a proper choice of the wavelengths used for the pump and DFWM beams, the dynamics of ion-pair states belonging to two different tiers are monitored.     

Stark quantum beat spectroscopy: The vibrational dependence of the dipole moment in the A1Σ+ state of BaO

The method of quantum beat spectroscopy following pulsed dye laser excitation is applied to measure electric field splittings in excited states of the ¹³⁸Ba¹⁶O molecule. Stark quantum beats were observed in the fluorescent decay of the A¹Σ⁺ (ν′ = 0, 1, 2, 3, J′ = 1) states. From the observed beat frequencies values of electric dipole moments in different vibrational states were derived. The results are: μ(ν′ = 0) = 2.98(7) D, μ(ν′ = 1) = 2.66(7) D, μ(ν′ = 2)3.15(8) D and μ(ν′ = 3) = 3.18(8) D.     

Variational calculation of specific, highly excited vibrational states in DFCO: comparison with experimental data

A stimulated emission pumping spectra of jet-cooled DFCO performed by Crane et al. (J. Mol. Spectrosc. 1997, 183, 273) has provided a great number of ro-vibrational lines up to 9000 cm(-1) of excitation energy. By combining a Jacobi-Wilson (JW) approach with a Davidson scheme, we calculate the lines provided by the experiment up to 9000 cm(-1) using an ab initio global potential energy surface (PES) developed by Kato et al. (J. Chem. Phys. 1997, 107, 6114). Comparisons between experimental and calculated data provide a critical test of the quality of the PES used. We show that the variational calculated energies can be efficiently corrected by taking into account the error observed for the A' fundamental transitions nu(i) (i = 1, ..., 5) and the first overtone 2nu(6). A detailed analysis of the eigenstates obtained by the calculation allows one to quantify the coupling between the different modes. Such an information is essential to understand and predict the energy flow through a DFCO molecule that is initially excited.     

Relaxation in excited vibrational levels of NH3 by infrared triple-resonance spectroscopy

A two step optical pumping technique in combination with transient diode laser absorption is described which provides a powerful tool for preparing sel     

One- and two-photon spectroscopy of highly excited states of alkali-metal atoms on helium nanodroplets

Alkali-metal atoms captured on the surface of superfluid helium droplets are excited to high energies (≈3?eV) by means of pulsed lasers, and their laser-induced-fluorescence spectra are recorded. We report on the one-photon excitation of the (n+1)p←ns transition of K, Rb, and Cs (n=4, 5, and 6, respectively) and on the two-photon one-color excitation of the 5d←5s transition of Rb. Gated-photon-counting measurements are consistent with the relaxation rates of the bare atoms, hence consistent with the reasonable expectation that atoms quickly desorb from the droplet and droplet-induced relaxation need not be invoked.     

Infrared vibrational spectroscopy of cis-dichloroethene in Rydberg states

We have measured the infrared (IR) vibrational spectrum for cis-dichloroethene (cis-ClCH[Double Bond]CHCl) in excited Rydberg states with the effective principal quantum numbers n(*)=9, 13, 17, 21, 28, and 55 using the vacuum ultraviolet-IR-photoinduced Rydberg ionization (VUV-IR-PIRI) scheme. Although the IR frequencies observed for the vibrational bands nu(11) (*) (asymmetric C-H stretch) and nu(12) (*) (symmetric C-H stretch) are essentially unchanged for different n(*) states, suggesting that the IR absorption predominantly involves the ion core and that the Rydberg electron behaves as a spectator; the intensity ratio for the nu(11) (*) and nu(12) (*) bands [R(nu(11) (*)nu(12) (*))] is found to decrease smoothly as n(*) is increased. This trend is consistent with the results of a model ab initio quantum calculation of R(nu(11) (*)nu(12) (*)) for excited cis-ClCH[Double Bond]CHCl in n(*)=3-18 states and the MP26-311++G(2df,p) calculations of R(nu(11)nu(12)) and R(nu(11) (+)nu(12) (+)), where R(nu(11)nu(12))[R(nu(11) (+)nu(12) (+))] represents the intensity ratio of the nu(11)(nu(11) (+)) asymmetric C-H stretching to the nu(12)(nu(12) (+)) symmetric C-H stretching vibrational bands for cis-ClCH[Double Bond]CHCl (cis-ClCH[Double Bond]CHCl(+)). We have also measured the IR-VUV-photoion (IR-VUV-PI) and IR-VUV-pulsed field ionization-photoelectron depletion (IR-VUV-PFI-PED) spectra for cis-ClCH[Double Bond]CHCl. These spectra are consistent with ab initio calculations, indicating that the IR absorption cross section for the nu(12) band is negligibly small compared to that for the nu(11) band. While the VUV-IR-PIRI measurements have allowed the determination of nu(11) (+)=3067+/-2 cm(-1), nu(12) (+)=3090+/-2 cm(-1), and R(nu(11) (+)nu(12) (+)) approximately 1.3 for cis-ClCH=CHCl(+), the IR-VUV-PI and IR-VUV-PFI-PED measurements have provided the value nu(11)=3088.5+/-0.2 cm(-1) for cis-ClCH=CHCl.