Dispersed Fluorescence Spectra Research Articles

Conformational preference of 2-(4-methoxyphenyl)ethanol studied by supersonic jet spectroscopy: Intramolecular OH/π interaction.

A π-type hydrogen bonding between the OH group and the π electron is a crucial factor for the conformational preference of the molecular structure with a flexible group. However, the information on the effect of the substituent on the OH/π interaction is insufficient. The laser-induced fluorescence (LIF) excitation, the dispersed fluorescence (DF), the IR-UV hole-burning, and the IR dip spectra of jet-cooled 2-(4-methoxyphenyl)ethanol were measured for the first time. Almost all bands observed in the spectral region of 35 550-36 500cm-1 in the LIF excitation spectrum were successfully assigned with the DF and the IR-UV hole-burning spectra coupled with the quantum chemical calculation at M06-2x/6-311G and MP2/6-311G levels. Five conformers were found in the LIF excitation spectrum. The most stable conformer was Ggπ, and the second most stable conformer was Ggπ' (the trans rotamer of the methoxy group for Ggπ). Ggπ and Ggπ' had the OH group directed toward the π electron system of the benzene ring. The OH stretching frequency of Ggπ/Ggπ' of MPE in the IR dip spectra was red-shifted against that of Ggπ of phenylethanol, indicating that the introduction of the methoxy group would enhance the intramolecular OH/π interaction. In addition, the torsional vibration between the benzene ring and the side chain (-CH2CH2OH) (mode 63) was observed in the DF spectra of the Ggπ-00 and Ggπ'-00 band excitation, but their intensities were rather different, resulting from the different orientation of the OH group for each conformer toward the π electron system. The methoxy group would increase the negative charge on the benzene ring and would enhance the intramolecular OH/π interaction through the electrostatic interaction.

Genetic algorithm for obtaining potential energy curve of diatomic molecules based on dispersed fluorescence spectra

The method for reconstruction of an adiabatic potential energy curve from experimental dispersed fluorescence spectra has been developed. The novelty of the method relies on a unique approach of simultaneous use of bound rightarrow bound and bound rightarrow free parts of the spectrum. The method is based on the Genetic Algorithm (GA) procedure and determines potential energy curve integrally, below and above the dissociation energy limit. The method was tested on the artificially generated reference spectrum as well as experimental spectrum of G0_u^+(upsilon ^{prime }=39) rightarrow X0_g^+ transition in Hg_2. The tests show very good accuracy of simulation based on GA results with artificially generated reference spectrum as well as with the experimental one.

Cryogenic Ion Fluorescence Spectroscopy: FRET in Rhodamine Homodimers and Heterodimers.

The internal electronic communication between two or more light-absorbers is fundamental for energy-transport processes, a field of large current interest. Here we have studied the intrinsic photophysics of homo- and heterodimers of rhodamine cations where just two methylene units bridge the dyes. Gas-phase experiments were done on frozen molecular ions at cryogenic temperatures using the newly built LUNA2 mass spectroscopy setup in Aarhus. Both absorption (from fluorescence excitation) and dispersed-fluorescence spectra were measured. In the gas phase, there is no dielectric screening from solvent molecules, and the effect of charges on transition energies is maximum. Indeed, bands are redshifted compared to those of monomer dyes due to the electric field that each dye senses from the other in a dimer. Importantly, also, as two chemically identical dyes in a homodimer do not experience the same field along the long axis, each dye has separate absorption. At low temperatures, it is therefore possible to selectively excite one dye. We find that fluorescence is dominantly from the dye with the lowest transition energy no matter which dye is photoexcited. Hence our work unequivocally demonstrates Förster Resonance Energy Transfer even in homodimers where one dye acts as donor and the other as acceptor.

Electronic Spectroscopy of Jet-Cooled NdO

Chemi-ionization reactions of the type M + O → MO+ + e- (M = Nd or Sm) are currently being investigated as a method to artificially increase the electron density in the ionosphere for control of micro- and radio wave propagation. Experiments involving the release of atomic Nd into the upper atmosphere have resulted in the production of a cloud that, on excitation by solar radiation, emits green light. It has been assumed that NdO was the carrier of this emission, but the existing spectroscopic data needed for this attribution is lacking. While the electronic spectrum of NdO has been well-characterized at wavelengths greater than 590 nm, relatively little spectroscopic data exist for emission wavelengths in the blue-green spectral range. In this study, spectra for jet-cooled NdO were recorded over the range 15,500-21,000 cm-1. Rotationally resolved laser induced fluorescence and vibronically resolved dispersed laser-induced fluorescence spectra were recorded, and nine new electronically excited states were identified. The data indicate that the electronic spectrum of NdO has relatively few allowed transitions in the green spectral range, casting doubt on the assignment of the Nd high-altitude release cloud green emission to NdO.

Cryogenic fluorescence spectroscopy of oxazine ions isolated in vacuo.

Recent developments in fluorescence spectroscopy have made it possible to measure both absorption and dispersed fluorescence spectra of isolated molecular ions at liquid-nitrogen temperatures. Absorption is here obtained from fluorescence-excitation experiments and does not rely on ion dissociation. One large advantage of reduced temperature compared to room-temperature spectroscopy is that spectra are narrow, and they provide information on vibronic features that can better be assigned from theoretical simulations. We report on the intrinsic spectroscopic properties of oxazine dyes cooled to about 100 K. They include six cations (crystal violet, darrow red, oxazine-1, oxazine-4, oxazine-170 and nile blue) and one anion (resorufin). Experiments were done with a home-built setup (LUNA2) where ions are stored, mass-selected, cooled, and photoexcited in a cylindrical ion trap. We find that the Stokes shifts are small (14-50 cm-1), which is ascribed to rigid geometries, that is, there are only small geometrical changes between the electronic ground and excited states. However, both the absorption and the emission spectra of darrow-red cations are broader than those of the other ionic dyes, which is likely associated with a less symmetric electronic structure and more non-zero Franck-Condon factors for the vibrational progressions. In the case of resorufin, the smallest ion under study, vibrational features are assigned based on calculated spectra.

Electronic, vibrational, and rotational analysis of 1,2-benzanthracene by high-resolution spectroscopy referenced to an optical frequency comb.

The electronic and vibrational structures of 1,2-benzanthracene-h12 (aBA-h12) and 1,2-benzanthracene-d12 (aBA-d12) were elucidated by analyzing fluorescence excitation spectra and dispersed fluorescence spectra in a supersonic jet on the basis of DFT calculation. We also observed the high-resolution and high-precision fluorescence excitation spectrum of the S1←S000 0 band, and determined the accurate rotational constants in the zero-vibrational levels of the S0 and S1 states. In this high-resolution measurement, we used a single-mode UV laser whose frequencies were controlled with reference to an optical frequency comb. The inertial defect is negligibly small, the molecule is considered to be planar, and the obtained rotational constants were well reproduced by the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculation. Both a-type and b-type transitions are found to be included in the rotationally resolved spectrum, and the a-type contribution is dominant, that is, the transition moment is nearly parallel to the long axis of the aBA molecule. We concluded that the S1 state is mainly composed of the Φ(B) configuration. The observed fluorescence lifetime (106ns) is considerably longer than that of the Φ(A) system, such as anthracene (18ns). The transition moment for the lower state of mixed states becomes small, reflecting a near-cancelation of the contributions from the parts of the wavefunction corresponding to the two electronic configurations. The bandwidth of the S2 ← S0 transition is large, and the structure is complicated. It is attributed to vibronic coupling with the high vibrational levels of the S1 state.

Rotational and deperturbation analysis of the interacting A2Π1/2, v = 11 ∼ B2Σ+, v = 6 states of yttrium monoxide (YO) molecule

The YO molecules in gas-phase were formed by the reaction of the laser produced yttrium plasma with molecular oxygen and subsequently cooled by free-jet expansion. The YO molecules were studied by laser-induced excitation and dispersed fluorescence (DF) spectroscopy at 0.1 cm-1 spectral resolution. The B2Σ+ state was observed in vibrations v=5 and 6 from the X2Σ+ ground state. The anomalously low spin-rotation constant of the B2Σ+, v=6 level compared to the v=0-5 vibrational levels of the B state indicated perturbation. Investigation of the wavelength filtered excitation spectra led to the observation of the A2Π1/2, v=11 spin-orbit component lying 28.5 cm-1 below the B2Σ+, v=6 state. The deperturbation analysis of the interacting pair of B2Σ+, v=6 ∼ A2Π1/2,v=11 states was carried out by incorporating the spin-orbit, spin-electronic and L-uncouple interaction parameters as off-diagonal matrix elements in the 2Σ+-2Π Hamiltonian. The molecular constants of v=11 of the A and v=6 of the B states followed the vibrational trend after deperturbation. The e-parity level of the B2Σ+, v=6 and A2Π1/2, v=11 crossed after J=25.5 and deperturbation analysis estimated J-dependent configuration mixing up to ∼50% for the e-parity and 16% for the f-parity levels. The value of the configuration mixing coefficient of the interacting A and the B states, obtained from the intensity analysis of the observed vibronic bands in the DF spectra, is in agreement with the depertubation analysis. In addition, the Ω=½ spin-orbit components of the A2Π state was observed in v=12 and 13 vibrations and were found to be unperturbed.

Fluorescence Excitation and Dispersed Fluorescence Spectra of the 1-Hydronaphthyl Radical (1-C10H9) in Solid para-Hydrogen.

Matrix isolation spectroscopy with para-hydrogen (p-H2) has previously been employed to record IR absorption spectra of hydrogenated and protonated polycyclic aromatic hydrocarbons (PAHs), prospective carriers of unidentified infrared and diffuse interstellar bands. Despite the promising prospects of p-H2 as matrix host, especially the rather weak interaction with the guest molecules and the resulting small matrix shifts, p-H2 matrix isolation spectroscopy has rarely been applied to study electronic transitions of guest molecules. Here, we present the dispersed fluorescence and fluorescence excitation spectrum of the 1-hydronaphthyl radical (1-C10H9) isolated in solid p-H2. We observed a strong 000 band associated with the electronic transition to the first excited electronic state at 18881 cm-1, red-shifted by ∼68 cm-1 relative to a value reported for jet-cooled 1-C10H9. From a comparison of our experimental results to simulated vibrationally resolved electronic absorption and emission spectra computed on the basis of (TD-)DFT geometry optimizations and scaled harmonic vibration calculations using the FCclasses code, we derived assignments for observed vibronic transitions. The dispersed fluorescence spectrum of 1-C10H9 is new; it complements the infrared spectrum and identified many vibrational modes unidentifiable with infrared. The excitation spectrum covers a much wider spectral range than previous reports. We compare the excitation spectrum in solid p-H2 to the reported electronic absorption spectrum of jet-cooled gaseous 1-C10H9 and that of 1-C10H9 isolated in solid Ne to assess the influence of p-H2 as a matrix host on the electronic transition of 1-C10H9 and discuss a potential contribution of 1-C10H9 to the diffuse interstellar bands.

Electronic Spectroscopy of SmO in the 645 to 670 nm Range.

The associative ionization reaction Sm + O → SmO+ + e- is being investigated as an electron source that could transiently modify high-altitude electron densities via Sm vapor release. Electronic spectra have been obtained from tests where sounding rockets released Sm vapor, but the interpretation of these results has been hampered by the limited laboratory spectral data available for both SmO and SmO+. The present study extends the spectroscopic characterization of SmO in the 645-670 nm range, where the field data show the most prominent molecular emission features. Rotationally resolved excitation spectra, dispersed laser-induced fluorescence spectra, and fluorescence decay lifetimes are reported. The results are consistent with the assignment of a subset of the red-region bands to configurational transitions of the form Sm2+(4f56s)O2- ↔ Sm2+(4f55d)O2-. Analysis of the excited state hyperfine structure supports this configurational description.

Simulation of the dispersed fluorescence spectrum of the NO[formula omitted][formula omitted] origin vibronic band

A vibronic Hamiltonian and transition dipole operator parametrized by high-level equation-of-motion coupled-cluster calculations are used as a basis for predicting the dispersed fluorescence spectrum of the B̃−X̃ origin band in the nitrate radical (NO3). The position and intensities of transitions to ground state vibrational levels observed in the photodetachment spectrum of the NO3 anion have previously been predicted to high fidelity with this Hamiltonian; it is expected that it also offers a basis for accurate prediction of the dispersed fluorescence spectrum. Comparison to experimental spectra provides considerable insight into various assignments. Significantly, this work joins a growing body of research that supports reassignment of the ground state ν3 vibrational fundamental to the region between 1050–1060 cm−1, which is more than 400 cm−1 below the feature to which it has traditionally been assigned. The in-plane vibrational levels below 2000 cm−1 are reviewed, with theory and experiment agreeing to within 25 cm−1 for all that have been observed experimentally. Finally, the various vibronic coupling mechanisms that affect the ground state energy levels of NO3 are summarized, and a discussion is provided about how the Lanczos algorithm can be used to efficiently calculate the dispersed fluorescence spectrum of the B̃−X̃ origin band.

Infrared and Laser-Induced Fluorescence Spectra of Sumanene Isolated in Solid para-Hydrogen.

The para-hydrogen (p-H2) matrix-isolation technique has been scarcely used to record electronic absorption and emission spectra. It is expected that its small matrix shifts due to diminished molecular interactions and the softness of the lattice might be advantageous to help identify the carriers of the diffuse interstellar bands. In this article, we present infrared, fluorescence excitation, and dispersed fluorescence spectra of sumanene (C21H12), a bowl-shaped polycyclic aromatic hydrocarbon and a fragment of C60, isolated in solid p-H2. The recorded vibrational wavenumbers from infrared and dispersed fluorescence agree with the scaled harmonic vibrational wavenumbers calculated with the B3PW91/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) methods. The recorded fluorescence excitation spectra are consistent with the spectra of jet-cooled gas-phase C21H12 reported previously by Kunishige et al. We found a rather small matrix shift of 55 cm-1 for the S1-S0 electronic transition origin located at 27 888 cm-1. Vibrational wavenumbers associated with the S1 state of C21H12 inferred from the experimental spectrum can be assigned mostly to fundamental normal modes; they are in satisfactory agreement with scaled harmonic vibrational wavenumbers calculated at the TD-B3PW91/6-311++G(2d,2p) level of theory. Significantly more vibrational modes of the S1 state were identified as compared with those in the reported gas-phase work. The potential of p-H2 matrix-isolation spectroscopy to provide electronic excitation spectra suitable for comparison to astronomical observations is discussed by comparing the spectra of C21H12 isolated in solid p-H2 and in solid Ne, a matrix host commonly employed in astrochemistry.

Laser-induced fluorescence spectroscopy of the B 5Π-1 – X 5Π-1 system of the chromium monosulfide molecule

Laser induced fluorescence and dispersed fluorescence spectroscopy was used to investigate the B 5Π-1 – X 5Π-1 system of the chromium monosulfide molecule. The rotational constant and Λ-doubling parameter of B 5Π-1 (v′ = 7), as a newly observed upper vibrational level, were obtained from the rotationally resolved laser excitation spectrum. For the ground X 5Π-1 state, the vibrational frequency and vibrational anharmonicity constant were experimentally determined for the first time from the dispersed fluorescence spectrum. In addition, the lifetimes of the upper B 5Π-1 (v′ = 0 − 7) levels were measured by fitting the time-dependent fluorescence decay.

Radiative force from optical cycling on magnesium monofluoride

We demonstrate radiative force deflection by using an optical cycling of the $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{1/2}^{+}\ensuremath{-}A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}$ electronic transition in diatomic molecule magnesium monofluoride (MgF). For the (0,0) and (0,1) bands of the electronic transition, the Franck-Condon factors---obtained by the dispersed laser-induced fluorescence spectrum---are ${f}_{00}=0.972$ and ${f}_{01}=0.028$, which suggests that the vibrational branching is quasiclosed. Furthermore, the dark Zeeman sublevels are destabilized by applying an external magnetic field. The cycling fluorescence is clearly observed to reveal that the molecular beam is deflected by 4.9 mm via scattering $\ensuremath{\sim}200$ photons per molecule. This work is encouraging toward laser cooling and magneto-optical trapping of MgF molecules.

Deperturbation analysis of the interacting C2Π1/2 (v=5), and D2Σ+ (v=1) levels of ScO

Perturbations have been observed between the C2Πi ∼ D2Σ+ pair of interacting states of ScO molecule in the 28,000−30,060 cm-1 region using jet-cooled laser-induced fluorescence spectroscopy at 0.04 cm-1 resolution. The interactions among the D2Σ+, v = 1 and C2Πi, v = 5 states are manifested in irregularity in rotational constants, dispersed fluorescence spectra and relevant Franck-Condon overlaps. The perturbations among these states are understood in terms of homogeneous spin-orbit, spin-electronic and heterogeneous L-uncoupling interactions between the C2Πi ∼ D2Σ+ states. The deperturbed molecular constants of the C2Πi, v = 5 and D2Σ+, v = 1 states have been determined by fitting the observed rovibronic transition wavenumbers to these excited states from the X2Σ+ ground state. The deperturbed position of the D2Σ+, v = 1 state lies only 1.5 cm-1 above the C2Π1/2, v = 5 component and the states interact severely, being pushed apart by 18 cm-1. In addition, the D2Σ+ state is observed in the v = 2 − 4 vibrational levels, which are found to be unperturbed. The deperturbed molecular constants of the vibrational levels of the C2Πi, and D2Σ+ states found in the present and our earlier reported work are used to generate Rydberg-Klein-Rees (RKR) potential curves. Subsequently, the vibrational overlap 〈vΠ|vΣ〉, and radial integrals BvΠ,vΣ, between the C2Πi and D2Σ+ states are computed and used to determine the pure electronic matrix elements connecting the electronic wavefunctions of these states.

Two-color resonance enhanced multiphoton ionization spectroscopy of o-hydroxybenzonitrile and Franck-Condon simulation

The cyano group is a typical electron-withdrawing group, which has aroused the interest of relevant researchers. Many papers reported the dispersed fluorescence spectra of o-hydroxybenzonitrile, its dimers, and complexes with small molecules, aiming to study the intermolecule hydrogen bond and the vibration features of the electronic ground state. There are also reports on using fluorescence excitation spectra to study excited state vibrations, but no report on the systematical analyzing of the vibration features of excited state spectra. Compared with fluorescence spectroscopy, resonance enhanced multiphoton ionization (REMPI) spectroscopy detects ions to obtain excited state energy level data, which has mass-resolution capability, and eliminates the interference of impurities with different charge-to-mass ratios. The strong electron-withdrawing ability of cyano group results in higher ionization energy for molecules containing cyano groups. Many REMPI experiments on benzonitrile derivatives require two-color lasers. In this paper, two-color resonance enhanced two-photon ionization experiment is performed by using a home-made linear time-of-flight mass spectrometer, and the vibration-resolved REMPI spectrum of o-hydroxybenzonitrile is obtained for the first time. Combining the high-precision density functional theory calculations with the Franck-Condon spectral simulations, the spectral characteristics are analyzed in detail, and a large number of fundamental, overtone and combined vibrations are found. The spectral assignment is carried out as accurately as possible. Most of the fundamental vibrations located at ring are assigned to the in-plane distortion or swing of the ring, which is related to the expansion of the ring during the molecular excitation. Theoretical and experimental results show that the low-frequency signal of REMPI spectrum is strong, the background is low, the band is less, and the resolution is good. As the vibration frequency increases, the signal changes in the worse direction. This is because the low-frequency spectrum mainly comes from the low-frequency fundamental vibrations and a little contribution from overtones. As the vibration frequency increases, the contributions from overtone and combined vibrations gradually increase, resulting in dense bands and low resolution. Theoretical calculations show that the high-order vibration and combination of multi-mode vibrations usually have a lower Franck-Condon factor, so the signal gradually becomes weak as the frequency increases, and the signal-to-noise ratio becomes worse.

Laser-induced fluorescence experimental spectroscopy and theoretical calculations of uranium monoxide

As a model molecule of actinide chemistry, UO molecule plays an important role in understanding the electronic structure and chemical bonding of actinide-containing species. We report a study of the laser-induced fluorescence spectra of the U16O and U18O using two-dimensional spectroscopy. Several rotationally resolved excitation spectra were investigated. Accurate molecular rotational constants and equilibrium internuclear distances were reported. Low-lying electronic states information was extracted from high resolution dispersed fluorescence spectra and analyzed by the ligand field theory model. The configuration of the ground state was determined as U2+(5f37s)O2−. The branching ratios, and the vibrational harmonic and anharmonic parameters were also obtained. Radiative lifetimes were determined by recording the time-resolved fluorescence spectroscopy. Transition dipole moments were calculated using the branching ratios and the radiative lifetimes. These findings were elucidated by using quantum-chemical calculations, and the chemical bonding was also analyzed. The findings presented in this work will enrich our understanding of actinide-containing molecules.

Jet cooled laser-induced fluorescence spectroscopy of tantalum monocarbide: Observation of the ground state vibrations and the low-energy states

• The equilibrium vibrational harmonic wavenumber, ω e for the ground state determined • Present ω e is more accurate and smaller by 28% from the earlier reported value • New assignments of the excitation bands • Low-energy excited states observed and tentatively assigned Laser-induced excitation and dispersed fluorescence (DF) spectra of TaC molecule, produced in laser vaporization free-jet apparatus, were studied to investigate the electronic structure. The DF from the earlier reported and newly assigned bands showed the ground state vibrational progression v = 0−3 and 5. Further, the observation and rotational analysis of the hot band from v = 1 of the ground state confirmed the T v = 1 = 769.108 ( 9 ) c m − 1 . The analysis of the vibrational and band origin data yielded the harmonic frequency ω e = 769.1(1) cm −1 for the X 2 Σ + ground electronic state. This value is distinctly different from the earlier reported value of 1064 cm −1 determined from the anion-photoelectron spectroscopy work (Phys. Rev. A 92 (2015) 042503). Additionally, the reasonably intense dispersed fluorescence peaks between the displacement wavenumber 2400 to 5900 cm −1 are tentatively assigned to low-lying states predicted by the earlier ab initio studies.

Spectroscopic Study of the B 1Π State of NaH.

In this study, the B1Π excited state of NaH has been experimentally studied for the first time. Pulsed laser-induced fluorescence excitation spectroscopy was used to investigate the B1Π electronic state of NaH. A total of 48 ro-vibronic transitions were observed, including within the B–X (0–0) and B–X (0–1) transition bands. Only one B-state vibrational level was identified, and a series of PQR lines, with eight e-parity and eight f-parity sublevels (v′ = 0, J′ = 1–8), were assigned. The level assignment was supported by a comparison of the experimental line positions with the ab initio calculations, the dispersed laser-induced fluorescence spectrum of the NaH B1Π → X1∑+ emission, and the V-type optical–optical double resonance spectra. The Dunham-type coefficients, the mean internuclear distance, the harmonic vibrational frequency ω, and the dissociation energies D0 and De of the B1Π state were determined.

Electronic Spectroscopy of cis- and trans-meta-Vinylbenzyl Radicals.

The D0(2A″)-D1(2A″) electronic transition of resonance-stabilized radical C9H9 isomers cis- and trans-meta-vinylbenzyl (MVB) has been investigated using resonant two-color two-photon ionization (R2C2PI) and laser-induced fluorescence. The radicals were produced in a discharge of m-vinyltoluene diluted in Ar and probed under jet-cooled conditions. The origin bands of the cis and trans conformers are at 19 037 and 18 939 cm-1, respectively. Adiabatic ionization energies near 7.17 eV were determined for both conformers from two-color ion-yield scans. Dispersed fluorescence (DF) was used to conclusively identify the cis-conformer: ground-state cis-MVB eigenvalues calculated for a Fourier series fit of a computed vinyl torsion potential are in excellent agreement with torsional transitions in the 19 037 cm-1 DF spectrum. R2C2PI features arising from cis- or trans-MVB were distinguished by optical-optical hole-burning spectroscopy and vibronic assignments were made with guidance from density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. There is a notable absence of mirror symmetry between excitation and emission spectra for several totally symmetric modes, whereby modes that are conspicuous in emission are nearly absent in excitation, and vice versa. This effect is largely ascribed to interference between Franck-Condon and Herzberg-Teller contributions to the electronic transition moment, and its pervasiveness a consequence of the low symmetry (Cs) of the molecule, which permits intensity borrowing from several relatively bright electronic states of A″ symmetry.

Pyritized preservation of chancelloriids from the Cambrian Stage 3 of South China and implications for biomineralization

The enigmatic Cambrian animal chancelloriids were discovered in a wide range of taphonomic settings; however, preservation of biomineralized sclerite microstructure was solely known from secondarily phosphatized skeletal remains. Here, we investigate a uniquely pyritized chancelloriid from the lower Cambrian Guojiaba Formation in southern Shaanxi Province, China, using a combination of advanced analytic techniques. Results of the energy dispersive spectroscopy (EDS), X-Ray Fluorescence (XRF), and Raman spectrum show that the sclerites and scleritomes are preserved as pyritized internal moulds with a calcitic outer layer. The outer layer enveloping the internal moulds likely represents the recrystallized counterpart of the original biomineralized sclerite wall. Distinctive fibrous microstructures are discovered in the sclerites, which echo the features seen in the phosphatized fossils of chancelloriids. The typical microstructure, along with the recrystallized calcite, corroborate the interpretation that chancelloriid sclerites were originally constructed by fibrous aragonite. The stability of the microstructure and mineral composition in both carbonate and siliciclastic backgrounds indicate that chancelloriids were adapted to exploit aragonitic fibres to build their skeletons regardless of the change of their living environments.