{"id":"df694d81-66b4-4963-a44c-b55e81fe1a89","arxiv_id":"2506.09906","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Thio- and selenofenchone were synthesized and characterized by microwave and infrared spectroscopy, and calculated spectra for telluro- and polonofenchone predict a strong nuclear-charge scaling of chirality-sensitive effects.","lead":"This paper synthesizes two heavier sulfur and selenium versions of the chiral molecule fenchone and measures their gas-phase rotational and infrared spectra. The data, plus calculations for tellurium and polonium versions, are meant to provide a tunable molecular family for studying how chirality effects grow with nuclear charge.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Table XIII's two-order-of-magnitude spread for 1-Po undermines the Z^5 scaling and the 10^-14 parity-violation estimate; the PV benchmark claim is not yet established.","rationale":"The paper's core experimental contribution—gas-phase MW structures and IR spectra for 1-S and 1-Se—is well supported by low-RMSD fits and consistent DFT comparisons. What makes the paper a 'benchmark system' for chirality studies, however, is the extension to systematic Z-dependent properties, chiefly parity violation. That extension depends on the Te/Po predictions and on the Z-scaling of Epv. The manuscript's own Table XIII shows a ~180-fold spread between HF and LDA for 1-Po, and the text admits that correlation and geometry effects could be important. Despite this, the conclusion quotes a ~10^-14 relative splitting derived from the HF endpoint. This is the weakest load-bearing assumption: if the true Epv is closer to LDA or outside the HF/LDA envelope, the 'sizable' parity-violation claim and the Z^5 scaling narrative collapse, even though the S/Se experimental benchmark remains valid. The reader identified the same DFT/VPT2 accuracy issue for Te/Po and the two-order-of-magnitude PV spread; my read agrees with that assessment. The recommended remedy—tempering the PV extrapolation and providing method-averaged estimates or uncertainties—is appropriate and does not change the conditional verdict.","tokens_in":51594,"tokens_out":4419,"duration_ms":49507,"concrete_test":"Compute Epv for 1-Po using a correlated relativistic method (e.g., ZORA or Dirac-based MP2/CCSD) on geometries optimized at the same two-component level used for the property, and repeat for 1-Se to calibrate against an experimentally determined r0 structure. If the correlated result lies within a factor of 2 of the HF value (5.7×10^-15 Eh), the 10^-14 estimate stands; if it falls near the LDA value (3.2×10^-17 Eh) or outside the HF/LDA envelope, the conclusion's Z^5/10^-14 claim should be tempered or removed.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central benchmark claim for systematic Z-dependence rests on the parity-violation extrapolation in §3.4/Table XIII. For 1-Po, HF, B3LYP and LDA give Epv = 5.7×10^-15, 9.1×10^-16 and 3.2×10^-17 Eh, a factor of ~180 between HF and LDA. The paper explicitly notes the spread becomes sizable and that correlation/geometry effects cannot be ruled out, yet the conclusion cites 'relative splittings of up to about 1e-14' based on the HF endpoint. If the true value is closer to the LDA value, the splitting is ~10^-16, and the Z^5 scaling (confirmed only on HF) is not a robust series property. The experimentally validated S/Se structures and spectra remain solid, but the 'benchmark' status for parity violation is not supported without a more reliable method or a stated uncertainty band.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports the synthesis of thiofenchone (1-S) and selenofenchone (1-Se), their gas-phase rotational and vibrational spectra, and a combined experimental/theoretical study of the series 1-O, 1-S, 1-Se, 1-Te, and 1-Po. Microwave spectroscopy with multiple isotopologues provides r0 structures whose C=X bond lengths agree with B3LYP/aug-cc-pVTZ(-PP) calculations to within 0.01–0.02 Å and with low RMSD fits (2.7–6.6 kHz). Gas-phase IR spectra are compared with harmonic (scaled by 0.968) and VPT2 anharmonic spectra, leading to assignments including C=X stretching and bending modes. For the unsynthesized telluro- and polonofenchone, predicted IR spectra are presented. The paper closes with exploratory parity-violating energy calculations (Table XIII) and concludes that the series is a promising benchmark for Z-dependent chirality studies, with relative parity-violating splittings potentially reaching about 10^-14 in polonofenchone.","tokens_in":51710,"tokens_out":3743,"duration_ms":49041,"significance":"If the central claim is taken as establishing a validated experimental platform, the paper's contribution is valuable: it provides new gas-phase structural data for heavy chalcogen analogues of fenchone, identifies C=X vibrational signatures across the series, and makes concrete predictions for Te and Po derivatives. The strengths are the high-quality microwave data (multiple isotopologues, low RMSD), the external rather than fitted scaling factor, and the explicit acknowledgment of VPT2 resonance problems. However, the parity-violation extrapolation is not robust: the spread among HF, B3LYP, and LDA for 1-Po spans nearly two orders of magnitude, and the stated Z^5 scaling is confirmed only at the HF level. The benchmark claim for parity violation therefore goes beyond what the present calculations support, and the predicted IR spectra of 1-Te and 1-Po inherit unquantified VPT2 artifacts already visible in 1-Se.","major_comments":[{"comment":"The conclusion that polonofenchone reaches relative parity-violating splittings of about 10^-14 rests on the HF value of 5.7×10^-15 Eh for 1-Po. The same table gives B3LYP 9.1×10^-16 Eh and LDA 3.2×10^-17 Eh, a spread of roughly a factor of 180. The Z^5 scaling is confirmed only on the HF level; B3LYP and LDA show substantially weaker growth. Since the text itself states that correlation and geometry-relaxation effects cannot be ruled out, the extrapolation to 10^-14 is not supported without an uncertainty band or a more reliable method. I recommend either presenting a conservative range (e.g., 10^-16 to 10^-14) or restricting the benchmark claim for parity violation to the experimentally characterized members.","section":"§3.4, Table XIII, Conclusion §4"},{"comment":"For 1-Se the VPT2 treatment freezes two C-H stretching modes and two bending modes, leading to a poorly reproduced C-H stretch region and a geminal-dimethyl doublet shifted by about 30 cm^-1, as the authors acknowledge. The predicted IR spectra of 1-Te and 1-Po are produced with the same DFT/VPT2 machinery but cannot be validated against experiment. The paper should state explicitly, in the sections presenting Figures 17–20 and Tables VI–VII and XI–XII, that these are unvalidated predictions whose accuracy is limited by the VPT2 artifacts already visible in 1-Se; otherwise the 'benchmark' status of the Te/Po predictions is overstated.","section":"§3.2.2, Figures 15–16, Tables V and X"},{"comment":"The single harmonic scaling factor of 0.968 is taken from an external benchmark for B3LYP/aug-cc-pVTZ (Ref 39). For Te and Po the calculations use aug-cc-pVTZ-PP with relativistic pseudopotentials, and the transferability of a factor calibrated for light-element systems is not demonstrated. Since the Te/Po band positions are central to the predicted series trend (Figure 9), the authors should either justify the transferability or provide unscaled harmonic and VPT2 values for the heavy members as a cross-check.","section":"§2.3, §3.2.1"}],"minor_comments":[{"comment":"The sentence 'Gas-phase MW spectra of 1-S and 1-S were recorded' should read '1-S and 1-Se'.","section":"§2.2, first paragraph"},{"comment":"Typos: 'champhor' should be 'camphor', 'Artimisinin' should be 'Artemisinin', and 'fudamental' should be 'fundamental'.","section":"§1 and §3.2.1"},{"comment":"The phrase 'mostly redistributed to ... combination bands ν69+ν55 and ν65+ν57 emerging at 1061 cm^-1' is clear, but the corresponding peak assignment in Table X would benefit from a direct indication of which experimental peaks (12–9) are matched by each calculated band.","section":"§3.2.2, paragraph beginning 'As for 1-S'"},{"comment":"The figure caption would be clearer if the data points for 1-O through 1-Po were labeled directly on the plot, since the left-to-right ordering is not immediately apparent from the symbol style alone.","section":"Figure 9"},{"comment":"The table would be more informative if it included the Z dependence explicitly (e.g., a column with X and nuclear charge) and if the HF, B3LYP, and LDA values were accompanied by the ratio to the 1-O value, which would make the deviation from Z^5 scaling quantitative.","section":"Table XIII"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. The experimental core—gas-phase microwave spectra, r0 structures, and IR assignments for thio- and selenofenchone—is new, well-executed, and trustworthy. The parity-violation section in §3.4 does not live up to the same standard, and the conclusion overstates it: the 10^-14 splitting for polonofenchone is the HF endpoint of a factor-180 spread across methods, not a robust prediction. That caveat is acknowledged inside the paper, but the abstract and conclusion still sell it as a benchmark.\n\nWhat is genuinely new: the first gas-phase rotational constants and r0 heavy-atom structures for 1-S and 1-Se, with RMSD fits in the 3–7 kHz range; the first gas-phase IR overview spectra and assignments for both; a modified selenation synthesis that improves yield to 45%; and the first DFT/VPT2 harmonic and anharmonic spectra for the unsynthesized 1-Te and 1-Po. The C=X bond lengths agree with DFT to 0.01–0.02 Å, and the 13C/34S/Se isotopologue fits give a well-determined backbone. The harmonic scaling factor 0.968 is taken from an external benchmark, not fitted, which keeps the IR comparison honest.\n\nSoft spots, in proportion. The VPT2 treatment freezes several resonant modes; in 1-Se this leaves the C–H stretch region poorly reproduced and shifts the geminal-dimethyl doublet by about 30 cm^-1. The paper says so openly, and the scaled harmonic spectra are still good, so this is a limitation, not a defect. The Te/Po spectra are unvalidated predictions, but they are labeled as such. The real issue is the PV extrapolation. Table XIII shows a spread from 5.7×10^-15 (HF) to 3.2×10^-17 (LDA) Eh for 1-Po. The conclusion's \"relative splittings of up to about 10^-14\" quotes only the HF endpoint. The stress-test note is right: the Z^5 scaling is not a robust series property at this level of theory, and \"benchmark\" is too strong a word for that section. The fix is straightforward—report the method spread as an uncertainty band, temper the conclusion, or relax the geometry on the two-component level. None of this breaks the S/Se experimental contribution.\n\nWho this is for: anyone working on chirality-sensitive spectroscopy, heavy-atom effects, or benchmark molecular series. The experimental sections deserve a serious referee and publication. The PV section needs revision before it can be taken at face value. I would accept this for peer review and recommend the authors soften the PV claims; the rest is solid.","headline":"The experimental S/Se spectroscopy is solid and new; the parity-violation extrapolation to 10^-14 relies on one endpoint of a factor-180 method spread and should be tempered before the paper is taken as a benchmark.","tokens_in":52404,"tokens_out":2428,"would_cite":true,"duration_ms":28326,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper establishes thio-, seleno-, telluro-, and polonofenchone as a tunable family for gas-phase chirality experiments, anchored by measured S/Se spectra and extending to predicted Te/Po members.","keywords":["chiral molecules","fenchone","chalcogenoketones","rotational spectroscopy","infrared spectroscopy","density functional theory","parity violation","photoelectron circular dichroism"],"falsifier":"Synthesize tellurofenchone or polonofenchone and measure its gas-phase infrared spectrum: if the most intense band assigned to C=Te stretching lies far from the predicted $1020\\,\\text{cm}^{-1}$, or C=Po stretching far from $965\\,\\text{cm}^{-1}$, the benchmark transferability of the DFT/VPT2 level is refuted. A high-resolution measurement of the C=Te stretching region could also test whether the predicted VPT2 combination bands near the fundamental are real or artifacts.","tokens_in":51340,"feed_emoji":"🧪","tokens_out":5262,"duration_ms":58745,"temperature":0.7,"pith_summary":"This paper aims to establish fenchone's heavier chalcogen derivatives, thiofenchone and selenofenchone, plus predictively telluro- and polonofenchone, as a bench-scale family for gas-phase studies of molecular chirality. Replacing the carbonyl oxygen with S, Se, Te, or Po changes the nuclear charge $Z$ at the chromophore while leaving the rigid bicyclic framework nearly untouched, which should amplify $Z$-sensitive effects such as electroweak parity violation and photoelectron circular dichroism. The authors synthesize and characterize 1-S and 1-Se, measure their gas-phase microwave and infrared spectra, and use DFT/VPT2 calculations to predict structures and vibrational spectra across the entire series. If the predictions hold, this compound family gives experimenters a systematically tunable knob, $Z$, for testing chirality-dependent physics in well-defined gas-phase conditions.","feed_headline":"Heavy chalcogen swaps make fenchone a Z-tunable chirality probe","feed_subtitle":"S/Se spectra anchor the series; predictions put Te and Po within reach of parity-violation searches.","key_machinery":"The central object is the chalcogenofenchone series $\\mathrm{1\\text{-}X}$, a fenchone cage with a single C=X double bond where X runs through O, S, Se, Te, and Po. The load-bearing mechanism is the monotonic change in C=X bond length, atomic mass, and force constant down the chalcogen column: it shifts the characteristic C=X stretching fundamental from above $1700\\,\\text{cm}^{-1}$ into the fingerprint region and, through the nuclear charge $Z$, scales the electroweak parity-violating potential. The methodological machinery is B3LYP/aug-cc-pVTZ(-PP) harmonic and VPT2 anharmonic force-field calculations, validated against microwave-derived $r_0$ structures and low-resolution FTIR spectra, together with quasi-relativistic zeroth-order regular approximation calculations of parity-violating potentials.","core_discovery":"The central claim is that heavier chalcogenofenchones $\\mathrm{1\\text{-}X}$ ($\\mathrm{X = S, Se, Te, Po}$) form a structurally rigid, volatile, and synthetically accessible series in which the C=X unit can be moved down the periodic table. The paper provides experimental rotational constants and effective $r_0$ structures for thiofenchone and selenofenchone, gas-phase IR assignments for fenchone, thiofenchone, and selenofenchone, and the first predicted equilibrium structures and IR spectra for telluro- and polonofenchone, along with exploratory parity-violating potentials. The measured C=S and C=Se bond lengths, $1.6341(30)\\,\\text{\\AA}$ and $1.773(21)\\,\\text{\\AA}$, validate the chosen DFT level, and the C=X stretching fundamental drops monotonically from $1742\\,\\text{cm}^{-1}$ in fenchone to a predicted $965\\,\\text{cm}^{-1}$ in polonofenchone. On the Hartree-Fock level the computed parity-violating energy differences grow by roughly five orders of magnitude from fenchone to polonofenchone, consistent with the expected $Z^5$ scaling, which is the property that makes the series attractive for future parity-violation searches.","pith_inferences":["If the DFT predictions survive direct measurement, the chalcogenofenchone series could serve as a calibration ladder for relativistic corrections in small chiral molecules, because the rigid cage keeps the geometry nearly fixed while only $Z$ changes.","The same $Z$-tunability could be extended to other terpenoid scaffolds, such as camphor derivatives, to test whether the observed scaling trends are specific to the C=X chromophore or generic to heavy-atom substitution near a stereogenic center.","A testable extension is to record the anharmonic C=X stretching region of tellurofenchone at high resolution; the VPT2-predicted intensity redistribution toward combination bands near the fundamental is a concrete, checkable prediction before any parity-violation search is attempted."],"forward_implications":["With thiofenchone and selenofenchone now structurally pinned by microwave data, their rovibrational spectra become realistic targets for high-resolution searches, and the demonstrated quantum-cascade-laser line width of $0.001\\,\\text{cm}^{-1}$ in fenchone shows the needed precision is in reach.","The predicted positions of the C=Te and C=Po stretching fundamentals at about $1020$ and $965\\,\\text{cm}^{-1}$ give concrete spectral windows for future synthesis and rotationally resolved infrared tests of the heavier members.","If the computed $Z^5$ scaling holds, parity-violating vibrational splittings should rise from roughly $\\Delta\\nu/\\nu \\approx 10^{-19}$ in fenchone to about $10^{-14}$ in polonofenchone, moving the effect closer to detectability.","The rigid C=X chromophore provides a common framework for photoelectron circular dichroism studies, with the chromophore absorption shifting from about $488\\,\\text{nm}$ in thiofenchone to about $625\\,\\text{nm}$ in selenofenchone, thereby complementing the parity-violation program.","The validated force-field level can be used to assign combination bands and overtones in the dense fingerprint region, which will be important for interpreting any future high-resolution spectrum of a heavy chalcogenofenchone."],"supporting_citations":[{"why":"Supplies the microwave-derived structure of fenchone used as the lightest reference point for the structural comparison across the chalcogen series.","marker":"[57]"},{"why":"Provides the crystal structure of fenchone used for condensed-phase comparison of the C=O bond length.","marker":"[52]"},{"why":"The Gaussian program package in which all DFT and VPT2 calculations were performed.","marker":"[38]"},{"why":"Source of the $0.968$ harmonic scaling factor used for direct comparison of computed and experimental infrared wavenumbers.","marker":"[39]"},{"why":"Introduces the zeroth-order regular approximation relativistic two-component Hamiltonians used for the parity-violating potential calculations.","marker":"[40]"},{"why":"Establishes the quasi-relativistic approach to molecular parity violation that underlies the $E_{pv}$ values reported here.","marker":"[41]"},{"why":"Provides the camphor parity-violating energy benchmark that places the fenchone $E_{pv}$ values in context.","marker":"[22]"},{"why":"The companion paper reporting excited-state assignment and photoelectron circular dichroism in chalcogen-substituted fenchones, which the present vibrational characterization supports.","marker":"[27]"},{"why":"SPFIT program used to fit the rotational constants of all observed isotopologues of thiofenchone and selenofenchone.","marker":"[54]"}],"fun_headline_variants":["S/Se fenchones measured; Te/Po predicted for Z-scaled chirality","Heavy chalcogen fenchones: a Z-tunable chirality probe","Fenchone's chalcogen series scales parity violation with Z^5","From S to Po: fenchone's heavy chalcogens tune chiral Z-probes"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The predictions for telluro- and polonofenchone rely on assuming that the same DFT/VPT2 level that works well for S and Se also describes the C=Te and C=Po force fields accurately enough for benchmark-quality spectra and parity-violating trends, even though no experiments exist for those compounds.","fun_headline_variants_meta":{"raw":{"variants":["S/Se fenchones measured; Te/Po predicted for Z-scaled chirality","Heavy chalcogen fenchones: a Z-tunable chirality probe","Fenchone's chalcogen series scales parity violation with Z^5","From S to Po: fenchone's heavy chalcogens tune chiral Z-probes"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001032,"raw_usage":{"total_tokens":4340,"prompt_tokens":932,"completion_tokens":3408,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":548,"completion_tokens_details":{"reasoning_tokens":3316}},"tokens_in":548,"tokens_out":3408,"duration_ms":29544,"temperature":1.0,"reasoning_tokens":3316,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T04:38:55.258515+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Synthesize tellurofenchone or polonofenchone and measure its gas-phase infrared spectrum: if the most intense band assigned to C=Te stretching lies far from the predicted $1020\\,\\text{cm}^{-1}$, or C=Po stretching far from $965\\,\\text{cm}^{-1}$, the benchmark transferability of the DFT/VPT2 level is refuted. A high-resolution measurement of the C=Te stretching region could also test whether the predicted VPT2 combination bands near the fundamental are real or artifacts.","supporting_citations":[{"cited_title":"Loru , author M","cited_arxiv_id":null,"evidence_quote":"Supplies the microwave-derived structure of fenchone used as the lightest reference point for the structural comparison across the chalcogen series."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the crystal structure of fenchone used for condensed-phase comparison of the C=O bond length."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The Gaussian program package in which all DFT and VPT2 calculations were performed."},{"cited_title":"Sinha , author S","cited_arxiv_id":null,"evidence_quote":"Source of the $0.968$ harmonic scaling factor used for direct comparison of computed and experimental infrared wavenumbers."},{"cited_title":"Berger , author N","cited_arxiv_id":null,"evidence_quote":"Establishes the quasi-relativistic approach to molecular parity violation that underlies the $E_{pv}$ values reported here."},{"cited_title":"Schwerdtfeger , author A","cited_arxiv_id":null,"evidence_quote":"Provides the camphor parity-violating energy benchmark that places the fenchone $E_{pv}$ values in context."},{"cited_title":"Excited state assignment and state-resolved photoelectron circular dichroism in chalcogen-substituted fenchones","cited_arxiv_id":"2503.14261","evidence_quote":"The companion paper reporting excited-state assignment and photoelectron circular dichroism in chalcogen-substituted fenchones, which the present vibrational characterization supports."}],"review_version":1}