Ab initio calculations have been performed to determine the structure and energies of the ground and first excited electronic states of bromine-and iodine-containing singlet carbenes. Effective core potential basis sets augmented with polarization functions were utilized at the CASSCF, CASPT2, and CISD levels of theory.Validation of the effective core potential basis sets for the ground and excited states of the singlet carbenes was carried out by comparison with previous results from all-electron basis set calculations. As was the case in previous studies of chlorine-and fluorine-containing halocarbenes, the bromine-and iodine-containing singlet carbenes are characterized by small bond angles in their ground states, ranging from 100°to 112°, and dramatically larger bond angles in their first excited states, ranging from 125°to 132°. This increase is due to the promotion of an electron from a carbon lone pair orbital coplanar with the carbon-halogen bonds to a carbon p-type orbital perpendicular to the bonds. Adiabatic transition energies for transitions from the ground to first excited state for the singlet carbenes determined at the CASPT2(18,12) and CISD levels range from 21 277 to 10 870 cm -1 and are in excellent agreement with experimental measurements where comparisons are available.

New upper and lower bounds to the van der Waals C6, C8, and C10 coefficients for hydrogen, noble gas, alkali, and alkaline earth atoms are determined by using Padé approximants to bound the dynamic multipole polarizabilities. Also, the nonadditive, three-body coefficients involving dipole, quadrupole, and octupole interactions are bounded.

Forensic laboratory backlogs are replete with suspected drug samples. Shifting analysis toward the point of seizure would save significant time and public funds. Moreover, a two-tiered identification strategy for controlled substance testing that relies on two independent, discerning methods could entirely circumvent the need for forensic laboratory testing. To this end, we coupled Raman spectroscopy and paper spray ionization mass spectrometry (PSI-MS) on a single instrumental platform. Both methods are capable of ambient analysis with fieldable instruments, yet Raman is often limited to bulk analysis. Critical to this work is the development of a gold nanoparticle (AuNP)-embedded paper swab to extend the capability of Raman spectroscopy to trace evidence via surface-enhanced Raman scattering (SERS). Plasmonic papers are characterized with respect to SERS signals and compatibility with PSI-MS analysis. Proof-of-principle is established with the identification of five representative drugs, and detection limits on the scale of 1–100 ng are achieved for both PSI-MS and SERS. The integrated SERS-PSI-MS system achieved 99.8% accurate chemical identification in a blind study consisting of 500 samples. Additionally, we demonstrate facile discrimination of several JWH-018 isomers via SERS even when MS and MS2 spectra are indistinguishable. Successful coupling of SERS and PSI-MS to enable on-site chemical analysis by two independent methods can potentially lead to a desirable paradigm shift in the handling of drug evidence.

Multireference configuration interaction (MRCI) calculations of the lowest singlet X(1A') and triplet ã((3)A'') states as well as the first excited singlet Ã((1)A'') state have been performed for a series of bromocarbenes: CHBr, CFBr, CClBr, CBr(2), and CIBr. The MRCI calculations were performed with correlation consistent basis sets of valence triple-ζ plus polarization quality, employing a full-valence active space of 18 electrons in 12 orbitals (12 and 9, respectively, for CHBr). Results obtained include equilibrium geometries and harmonic vibrational frequencies for each of the electronic states, along with ã((3)A'') ← X((1)A') singlet-triplet gaps and Ã((1)A'') ← X((1)A') transition energies. Comparisons have been made with previous computational and experimental results where available. The MRCI calculations presented in this work provide a comprehensive series of results at a consistent high level of theory for all of the bromocarbenes.

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