Infrared multiphoton dissociation (IRMPD) spectroscopy has been used to record IR signatures of chirality recognition in the protonated serine dimer and octamer in the 3200-3800 cm(-1) region. This is the first IRMPD study to investigate the heterochiral biomolecular system by utilizing the isotope-labelled species. Noticeable differences in the homo- versus heterochiral IRMPD spectra have been obtained experimentally for both the dimer and octamer. Different dissociation patterns have been noted not only between the homo- and heterochiral octamers, but also between the two -OH stretching vibrational bands of the same chirality species. Systematic theoretical searches have been carried out to identify the most stable conformers of both the homo- and heterochiral protonated serine dimer and octamer. The final geometry optimization and harmonic vibrational calculations have been performed at the MP2/6-311++G(d,p) level for the homo- and heterochiral protonated serine dimer and at the B3LYP/6-31G(d) level for the homo- and heterochiral protonated serine octamer. For the homo- and heterochiral dimer, good agreement between the experimental and theoretical spectra has been achieved and the major conformers have been identified. For the homo- and heterochiral octamer, the main IR features observed have been satisfactorily reproduced theoretically and the dominant conformers identified. More than one main conformer has been identified for the homochiral octamer. This conclusion has been further supported by the analysis of the wavelength specific dissociation products.

The electronic spectrum of copper hydrosulfide (CuSH) has been observed for the first time. CuSH and CuSD were produced in a pulsed discharge jet by the reaction of sputtered copper atoms with H(2)S or D(2)S. Strong laser-induced fluorescence bands observed in the 515-470 nm region were assigned as the ~A (1)A"-X (1)A' band system based on detailed rotational analysis and the correspondence with the predictions of our CCSD(T)6-311++G(3df,3pd) ab initio calculations. The laser-induced fluorescence and single vibronic level emission spectra consist primarily of a short progression in nu(3), the Cu-S stretching mode, indicative of only modest structural changes on electronic excitation. The rotational constants of four isotopomers of CuSH were used to determine effective zero-point structures in the combining states as r"(CuS)=2.0916(3) A, r"(SH)=1.364(3) A, theta"=93.5(3) degrees , r'(CuS)=2.172(3) A, r'(SH)=1.408(23) A, and theta'=93.5(24) degrees . A comparison of the ground state structures of the known metal hydrosulfides shows that they can be considered to be metal-substituted hydrogen sulfides. The electronic spectra and molecular structures of CuOH and CuSH are compared and contrasted.

Chirality recognition in the hydrogen-bonded glycidol···propylene oxide complex has been studied by using rotational spectroscopy and ab initio calculations. An extensive conformational search has been performed for this binary adduct at the MP2/6-311++G(d,p) level of theory and a total of 28 homo- and heterochiral conformers were identified. The eight binary conformers, built of the two dominant glycidol monomeric conformers, g-G+ and g+G-, were predicted to be the most stable ones. Jet-cooled rotational spectra of six out of the eight conformers were observed and unambiguously assigned for the first time. The experimental stability ordering has been obtained and compared with the ab initio predictions. The relative stability of the two dominant glycidol monomeric conformers is reversed in some cases when binding to propylene oxide. The contributions of monomeric energy, deformation energy, and binary intermolecular interaction energy to the relative stability of the binary conformers are discussed.

The (2)Delta(r)-X (2)Pi(r) band system of the jet-cooled arsenic dicarbide (C(2)As) free radical has been recorded by laser-induced fluorescence (LIF) techniques in the 685-588 nm region. The radical was produced in a pulsed electric discharge jet using a precursor mixture of AsCl(3) vapor and methane in high pressure argon. A series of weak bands involving all three excited state vibrations was observed for both (12)C(2)As and (13)C(2)As. High-resolution spectra of the (2)Pi(12) component of the 0(0)(0) bands of both isotopomers were rotationally analyzed, leading to the conclusion that the upper state is (2)Delta with a small spin-orbit splitting (A = 2.78 cm(-1)). Ground and excited state molecular structures of r(0)(")(CC,ab initio) = 1.2933 A, r(0)(")(CAs) = 1.734(4) A and r(0)(')(CC,ab initio) = 1.2276 A, r(0)(')(CAs) = 1.830(3) A were derived from the B values and our density functional predictions of the C-C bond lengths. Single vibronic level emission spectra were recorded for many of the LIF bands and these were used to obtain the ground state vibrational frequencies and spin-orbit splittings. These data were satisfactorily fitted to a Renner-Teller model which gave (12)C(2)As parameters of epsilon = 0.695(8), omega(1) = 1704.8(20) cm(-1), omega(2) = 161.6(8) cm(-1), omega(3) = 663.6(12) cm(-1), and a spin-orbit constant A = 857.7(11) cm(-1).

Subsequent to our spectroscopic detection of the C(2)X(X=P,As) free radicals [F. X. Sunahori et al., J. Am. Chem. Soc. 129, 9600 (2007)], we have studied the electronic spectrum of the (2)Delta(i)-X (2)Pi(r) system of the jet-cooled C(2)P free radical in the 490-630 nm region. The high-resolution laser-induced fluorescence spectrum of the two spin components of the 0(0) (0) band of (12)C(2)P has been recorded, and the rotational and spin-orbit coupling constants have been determined for both electronic states. The Renner-Teller effect has been observed in both the (2)Pi and the (2)Delta states, and the vibrational structure has been assigned. For the ground state, all of the observed levels up to 3500 cm(-1) were fitted with a standard Renner-Teller model. The excited (2)Delta state vibrational levels were successfully fitted using literature energy level expressions derived from perturbation theory, yielding vibrational and Renner-Teller parameters for both (12)C(2)P and (13)C(2)P. The molecular structure of C(2)P in the ground and excited states has also been estimated and compared to ab initio calculations and the geometries of similar molecules.