Fluorescence Depletion Spectroscopy Research Articles

Landé gJ - factors of Nb I levels determined by laser spectroscopy

Laser spectroscopy methods were used in the investigation of the Zeeman-hyperfine structure of 14 lines of atomic niobium in the visible region 585.279–637.481 nm. We used the laser induced fluorescence (LIF) method and for higher lying states the fluorescence depletion spectroscopy (FDS). The magnetic field of approximately 800G was generated by a permanent neodymium magnet. The source of niobium atoms was a hollow cathode discharge tube. We determined experimentally for the first time the Lande gJ-factor values for six levels. We also verified earlier experimental data on the hf structure as well as the experimental data from the NIST database regarding Lande gJ-factors. For four levels we have obtained more accurate results.

Laser spectroscopy used in the investigation of the Zeeman - hyperfine structure of vanadium

Laser spectroscopy methods were used in investigations of the Zeeman - hf structure of 17 lines of atomic vanadium in the visible green - red region 568.3 - 648.1 nm. We used two methods of laser spectroscopy: the laser induced fluorescence (LIF) and fluorescence depletion spectroscopy (FDS). A hollow cathode discharge tube was the source of vanadium atoms. Zeeman structure measurements were carried out using a permanent neodymium magnet generating a field of approximately 800 G. We determined A hfs constants for 7 levels and values of the Lande gJ factors for 10 levels. We also verified the previously determined gJ factors for 12 levels and 18 hfs constants.

Magnetic splitting of La I lines studied by means of fluorescence depletion spectroscopy

The fluorescence depletion spectroscopy (FDS) was used to study the structure of 11 La I lines in the visible green-red region 579.5–645.8 nm. A discharge tube with hollow cathode was the source of free La atoms. The measurements were carried out for two mutually perpendicular states of linear polarization of the laser light. The spectra were recorded in the presence of a magnetic field of about 800G. We determined Landé gJ factors for 7 levels, we improved the precision of the hyperfine structure (hfs) data for 6 even parity levels and we reanalyzed gJ data for several other levels of La I.

Observation of the shallow state of NaH.

The 2 1Π state of NaH has been observed up to the last bound vibrational level using pulsed optical-optical double resonance fluorescence depletion spectroscopy. A total of 20 rovibrational energy levels ( = 2-4 and J = 1-9) were assigned to this electronic state by means of comparing the successive rovibrational spectra to the eigenvalues of the ab initio potential energy curve. The decrease of background fluorescence near the atomic asymptotic limit Na(3d) + H(1s) is an indication of reaching the dissociation limit of the NaH 2 1Π state. Unobserved rovibrational levels ( = 0 and 1) are due to poor Franck-Condon overlap of 2 1Π ← A 1Σ+ transition within the accessible rovibrational levels of intermediate A 1Σ+ state of this work.

Observation of double-well potential of NaH C 1Σ+ state: Deriving the dissociation energy of its ground state.

Vibrational levels (v = 6-42) of the NaH C 1Σ+ state including the inner and outer wells and the near-dissociation region were observed by pulsed optical-optical double resonance fluorescence depletion spectroscopy. The absolute vibrational quantum number is identified by comparing the vibrational energy difference of this experiment with the ab initio calculations. The outer well with v up to 34 is analyzed using the Dunham expansion and a Rydberg-Klein-Rees (RKR) potential energy curve is constructed. A hybrid double-well potential combined with the RKR potential, the ab initio calculation, and a long-range potential is able to describe the whole NaH C 1Σ+ state including the higher vibrational levels (v = 35-42). The dissociation energy of the NaH C 1Σ+ state is determined to be De(C) = 6595.10 ± 5 cm-1 and then the dissociation energy of the NaH ground state De(X) = 15 807.87 ± 5 cm-1 can be derived.

Spectroscopic determination of the ground-state dissociation energy and isotopic shift of NaD.

Stimulated emission pumping with fluorescence depletion spectroscopy is used to determine the NaD X 1Σ+ ground-state dissociation energy and its isotopic shift. A total of 230 rovibrational levels in the range 9 ≤ v″ ≤ 29 and 1 ≤ J″ ≤ 11 are observed, where v″ = 29 is about 50 cm-1 below the dissociation limit. Analysis of the highest five vibrational levels yields the dissociation energy De = 15 822 ± 5 cm-1 with a vibrational quantum number at dissociation vD = 31.2 ± 0.1. The energy difference in the well depth of this isotopologue with respect to that of NaH is δDe = De(NaH) - De(NaD) = -7 cm-1. A new set of Dunham coefficients is derived to fit all the observed energy levels to within the experimental uncertainty.

Real-time monitoring of bacterial and organic pollution in a water stream by fluorescence depletion spectroscopy

We demonstrate an approach for a real-time, consumable-free optical system operating on a liquid jet which can be easily derived from the water distribution infrastructure. We apply a pump-probe scheme based on the acquisition and nanosecond manipulation of UV-excited fluorescence to increase the selective identification of bacterial against organic pollutants in water.

Laser spectroscopy of the Ã(2)Σ(+)-X̃(2)Πi band system of l-SiC3H.

The Ã(2)Σ(+)-X̃(2)Πi band system of l-SiC3H in the region 14,700-16,300 cm(-1) was re-investigated by laser induced fluorescence (LIF) and fluorescence depletion spectroscopy. Rotational analyses were made for three intense bands 0(0)(0), 4(0)(1), and 6(0)(1)7(0)(1) by observing high-resolution LIF excitation spectra. The determined rotational constants demonstrate that SiC3H is linear in the à state, as is the case in the X̃ state, and the observed band types are consistent with the vibrational assignments. The ν3(″) (C1-C2 stretch) level was identified in a newly observed dispersed fluorescence spectrum from the zero-vibrational level of the à state.

Spectroscopic study on the [formula omitted] transition of the trans-2-methylvinoxy radical

Electronic excitation spectra of the B̃2A″-X̃2A″ transition of the trans-2-methylvinoxy radical were observed in the region of 29000–32000cm−1 by laser-induced fluorescence and fluorescence depletion spectroscopy. Fourteen vibronic bands observed in the depletion spectrum were unambiguously identified to be originating from the radical. Dispersed fluorescence spectra from three different vibronic levels were also obtained, and a total of 69 emission bands were assigned, yielding the ground state vibrational constants.

Electronic spectroscopy of the HCCN radical

The Ã(3)A"-X̃(3)Σ(-) electronic transition of the HCCN∕DCCN radical was observed by laser-induced fluorescence spectroscopy. Rotationally resolved excitation spectra were observed for HCCN and DCCN, and effective molecular constants of the upper state were determined. The observed intensities of the rotational lines were anomalous, probably due to a level-dependent non-radiative decay process in the excited state. Fluorescence depletion spectroscopy was applied in order to observe non-fluorescent vibronic levels. A dispersed fluorescence spectrum was also observed to determine the vibrational level structure in the ground electronic state. The observed vibrational structures in the fluorescence depletion and dispersed fluorescence spectra were tentatively assigned based on the results of ab initio calculations.

Mechanisms of ultrafast fluorescence depletion spectroscopy and applications to measure slovation dynamics of coummarin 153 in methanol

Subpicosecond fluorescence depletion spectroscopy (FDS) was used to measure the solvation dynamics of coumarin 153 (C153) in methanol. The FDS mechanisms were discussed. A quasi-continuous model was used to describe the solvational relaxation of excited states. The perturbations of the probe pulse on the excited sample system, including up-conversion and stimulated emission, were sufficiently discussed. For a probe molecule used in the FDS experiment, ensuring that the up-conversion perturbation can be negligible is important. FDS was found to be a good technique for measuring the solvation dynamics of C153 in methanol.

Dissociation energy of the ground state of NaH

The dissociation energy of the ground state of NaH was determined by analyzing the observed near dissociation rovibrational levels. These levels were reached by stimulated emission pumping and fluorescence depletion spectroscopy. A total of 114 rovibrational levels in the ranges 9<or=v(")<or=21 and 1<or=J(")<or=14 were assigned to the X (1)Sigma(+) state of NaH. The highest vibrational level observed was only about 40 cm(-1) from the dissociation limit in the ground state. One quasibound state, above the dissociation limit and confined by the centrifugal barrier, was observed. Determining the vibrational quantum number at dissociation v(D) from the highest four vibrational levels yielded the dissociation energy D(e)=15 815+/-5 cm(-1). Based on new observations and available data, a set of Dunham coefficients and the rotationless Rydberg-Klein-Rees curve were constructed. The effective potential curve and the quasibound states were discussed.

Characterization of the outer well of NaH C 1Σ + state by fluorescence depletion spectroscopy

The outer well of the NaH C 1Σ + excited state was determined using pulsed optical–optical double resonance fluorescence depletion spectroscopy. The level-selected fluorescence of the A 1Σ + state is depleted back to the ground state when a probe laser excites the molecules to the C 1Σ + state. A total of 456 rovibrational levels, v = 5–33 and J = 1–11, were observed. A set of Dunham constants and the Rydberg–Klein–Rees (RKR) potential curve for the outer well were reported.

An experimental and theoretical study on vibrational structure in the B̃–X̃ transition of CH2CHS

An electronic excitation spectrum of the B̃–X̃ transition of the CH2CHS (vinylthio, thiovinoxy) radical was observed in the range of 21 800–23 400 cm−1 by fluorescence depletion spectroscopy. Vibrational assignments for the depletion spectrum were made with the help of a theoretical excitation spectrum computed from results of ab initio calculations. The previously observed emission spectrum [M. Nakajima et al., J. Chem. Phys. 126, 044307 (2007)] was also reassigned based on the present theoretical study. Rotational band contours observed in the depletion spectrum show a large variation due to a vibrational-level dependence of the excited state lifetime. However, no obvious vibrational mode dependence of the lifetime was observed.

Experimental and theoretical study of the rotational reorientation dynamics of 7-animocoumarin derivatives in polar solvents: hydrogen-bonding effects

The rotational reorientation dynamics of 7-aminocoumarin derivatives with different alkylation degrees in methanol, dimethylformamide, and dimethyl sulfoxide have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) spectroscopy. In addition to a long anisotropy decay time that accounts for the overall rotational relaxation of solutes, a short anisotropy decay time on the order of picoseconds or sub-picoseconds was also observed in hydrogen-bonding systems. Three types of hydrogen bonds involving the nitrogen lone pair, carbonyl group, and amino group of 7-aminocoumarin derivatives were denoted as types A, B, and C, respectively. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out to investigate the geometric structures of isolated coumarins and hydrogen-bonded complexes in the ground and excited states, respectively. According to our results and analysis, the rapid anisotropy decays observed here in hydrogen-bonding systems may be associated with the strengthening of hydrogen bonds B or C, or both in the excited state of hydrogen-bonded coumarin-solvent complexes, and are independent of the breaking of hydrogen bond A. The strengthening of hydrogen bond C in the excited state of 7-aminocoumarin-DMF and 7-aminocoumarin-DMSO complexes has been demonstrated theoretically for the first time. Further experimental studies would be crucial to confirm this observation.

Rotational reorientation dynamics of Rhodamine 700 in different excited states

The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S 1) and the fifth (S 5) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40–230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes–Einstein–Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S 5 are smaller than those in S 1, which is in accord with the predictions by the SED theory. In addition, for LD700 in S 5, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S 5 to S 1, and the rate of internal conversion was found to be sensitive to the solvent polarity.

Spectroscopy, dissociation dynamics, and potential energy surfaces for CN(A)−Ar

The A (2)Pi-X (2)Sigma(+) band system of CN-Ar has been examined using fluorescence depletion and action spectroscopy techniques. Eight vibronic bands of the complex were observed in association with the monomer 3-0 transition. Pump-probe measurements were used to characterize CN(A (2)Pi(32),nu=3) fragments from direct photodissociation of CN(A (2)Pi,nu=3)-Ar and CN(X (2)Sigma(+),nu=7) fragments from CN(A (2)Pi,nu=3)-Ar predissociation. The latter showed a marked preference for population of positive parity diatomic rotational levels. Bound state calculations were used to assign the A-X bands and to obtain fitted potential energy surfaces for the A state. The average potential obtained from fitting had a well depth of D(e)=137.8 cm(-1). High-level ab initio calculations were used to obtain equilibrium Jacobi coordinates of theta(e)=94 degrees and R(e)=7.25 bohr. The near-symmetric character of the fitted potential energy surface was consistent with the symmetry preference observed in the predissociation dynamics.

Rotational Reorientation Dynamics of Oxazine 750 in Polar Solvents

The rotational reorientation dynamics of oxazine 750 (OX750) in the first (with pump pulse at 660 nm) and a higher excited state (with pump pulse at 400 nm) in different polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) spectroscopy. In both excited states, three different anisotropy decay laws have been observed for OX750 in different solvents. Only in acetone and formamide could the anisotropy decays of OX750 be described by single-exponential functions, whereas the anisotropy decays have been found to exhibit biexponential behavior in other solvents. The slower anisotropy decay observed in all of the solvents has been assigned to the overall rotational relaxation of OX750 molecules, and a quantitative analysis of this time constant has been performed using the Stokes-Einstein-Debye hydrodynamic theory and the extended charge distribution model developed by Alavi and Waldeck. In both methanol and ethanol, a faster anisotropy decay on the order of picoseconds and a slower anisotropy decay on the hundreds of picoseconds time scale are observed. The most likely explanation for the faster anisotropy involves the rotation of the transition dipole moment in the excited state of OX750 resulting from the electron transfer (ET) reaction taking place from the alcoholic solvents to the OX750 chromophore. As a possible explanation, the wobbling-in-the-cone model has been used to analyze the biexponential anisotropy decays of OX750 in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The observed faster anisotropy decays on the hundreds of femtoseconds time scale in DMF and DMSO are ascribed to the wobbling-in-the-cone motion of the ethyl group of OX750, which is sensitive to the strength of the hydrogen bond formed between the solvent and the protonation site of OX750.

Site-Selective Photoinduced Electron Transfer from Alcoholic Solvents to the Chromophore Facilitated by Hydrogen Bonding: A New Fluorescence Quenching Mechanism

Solute-solvent intermolecular photoinduced electron transfer (ET) reaction was proposed to account for the drastic fluorescence quenching behaviors of oxazine 750 (OX750) chromophore in protic alcoholic solvents. According to our theoretical calculations for the hydrogen-bonded OX750-(alcohol)(n) complexes using the time-dependent density functional theory (TDDFT) method, we demonstrated that the ET reaction takes place from the alcoholic solvents to the chromophore and the intermolecular ET passing through the site-specific intermolecular hydrogen bonds exhibits an unambiguous site selectivity. In our motivated experiments of femtosecond time-resolved stimulated emission pumping fluorescence depletion spectroscopy (FS TR SEP FD), it could be noted that the ultrafast ET reaction takes place as fast as 200 fs. This ultrafast intermolecular photoinduced ET is much faster than the diffusive solvation process, and even significantly faster than the intramolecular vibrational redistribution (IVR) process of the OX750 chromophore. Therefore, the ultrafast intermolecular ET should be coupled with the hydrogen-bonding dynamics occurring in the sub-picosecond time domain. We theoretically demonstrated for the first time that the selected hydrogen bonds are transiently strengthened in the excited states for facilitating the ultrafast solute-solvent intermolecular ET reaction.

Observation of a new phosphorus-containing reactive intermediate: Electronic spectroscopy and excited-state dynamics of the HPBr free radical

The A (2)A(')-X (2)A(") electronic spectra of jet-cooled HPBr and DPBr have been obtained for the first time using the pulsed electric discharge technique with a precursor mixture of PBr(3) and H(2)/D(2). Laser-induced fluorescence and single vibronic level emission spectra gave the bending and P-Br stretching frequencies in the ground and excited states of both isotopomers. Rotational analyses of the HPBr and DPBr 0(0) (0) bands showed small spin splittings characteristic of a doublet-doublet transition of an asymmetric-top molecule. From the ground- and excited-state rotational constants, effective (r(0)) structures were derived with r(")(PH)=1.4307(86) A, r(")(PBr)=2.2021(9) A, and theta(")=95.2(8) degrees, and r(')(PH)=1.434(31) A, r(')(PBr)=2.1669(26) A, and theta(')=115.5(16) degrees . In a few favorable cases, further hyperfine splitting of the spin-rotation energy levels has been observed, due to the excited-state Fermi contact interaction of the unpaired electron with the spin magnetic moment of the (31)P nucleus, with a(F) (')=0.064(9) cm(-1) for HPBr. Fluorescence depletion spectroscopy and lifetime measurements indicate that higher vibrational levels of the A (2)A(') state are predissociated by a X (2)A(") dissociative continuum. CCSD(T)/aug-cc-pVTZ calculations predict that the most likely dissociation process is HPBr (X (2)A("))-->PH((3)Sigma(-))+Br((2)P(u)).