Electronic absorption and emission spectra have been investigated for cyanodiacetylene, HC(5)N, an astrophysically relevant molecule. The analysis of gas-phase absorption was assisted with the parallel rare gas matrix isolation experiments and with density functional theory (DFT) predictions concerning the excited electronic states. Mid-UV systems B (1)Delta<--X (1)Sigma(+) (origin at 282.5 nm) and A (1)Sigma(-)<--X (1)Sigma(+) (306.8 nm) were observed. Vibronic assignments have been facilitated by the discovery of the visible phosphorescence a (3)Sigma(+)<--X (1)Sigma(+) in solid Ar, Kr, and Xe. Phosphorescence excitation spectra, as well as UV absorption measurements in rare gas matrices, revealed the enhancement of A<--X transitions. The vibronic structure of dispersed phosphorescence spectra supplied new data concerning the ground state bending fundamentals of matrix-isolated HC(5)N. The experimental singlet-triplet splitting, 2.92 eV in Ar, closely matches the value of 3.0 eV predicted by DFT.

The infrared absorption spectra of matrix-isolated zinc phthalocyanine (ZnPc) and free-base phthalocyanine (H 2 Pc) have been recorded in the region from 400 to 4000 cm À1 in solid N 2 , Ar, Kr and Xe. Raman spectra have been recorded in doped KBr pellets. The isotopomers HDPc and D 2 Pc have been synthesised in an attempt to resolve the conflicting assignments that currently exist in the literature for the N-H bending modes in H 2 Pc spectra. A complete correlation between the vibrational modes of the three free-base isotopomers and ZnPc has been achieved. Comparison of the IR and Raman spectroscopic results, obtained with isotopic substitution and with predictions from large basis set ab initio calculations, allows identification of the in-plane (IP) and out-of-plane (OP) N-H bending modes. The largest IP isotope shift is observed in the IR at 1046 cm À1 and at 1026 cm À1 in Raman spectra while the largest effect in the OP bending modes is at 764 cm À1 . OP bending modes are too weak to be observed in the experimental Raman data. The antisymmetric N-H stretching mode is observed at B3310 cm À1 in low temperature solids slightly blue shifted from, but entirely consistent with the literature KBr data. With the exception of the N-H stretches, the recorded H/D isotope shifts in all the N-H vibrations are complex, with the IP bending modes exhibiting small n H /n D ratios (the largest value is 1.089) while one of the observed OP modes has a ratio o 1. DFT results reveal that the small ratios arise in particular from strong coupling of the N-H IP bending modes with IP stretching modes of C-N bonds. The unexpected finding of a n H /n D ratio smaller than one was analysed theoretically by examining the evolution of the frequencies of the free base by increasing the mass from H to D in a continuous manner. A consequence of this frequency increase in the heavier isotopomer is that the direction of the N-D OP bend is reversed from the N-H OP bend.

The absorption, emission and excitation spectra of ZnPc and H 2 Pc trapped in Ne, N 2 , Ar, Kr and Xe matrices have been recorded in the region of the Q states. A comparison of the matrix fluorescence spectra with Raman spectra recorded in KBr pellets reveals very strong similarities. This is entirely consistent with the selection rules and points to the occurrence of only fundamental vibrational transitions in the emission spectra. Based on this behaviour, the vibronic modes in emission have been assigned using results obtained recently on the ground state with large basis-set DFT calculations [Murray et al. PCCP, 12, 10406 (2010)]. Furthermore, the very strong mirror symmetry between excitation and emission has allowed these assignments to be extended to the excitation (absorption) bands. While this approach works well for ZnPc, coupling between the band origin of the S 2 (Q Y ) state and vibrationally excited levels of S 1 (Q X ), limits the range of its application in H 2 Pc. The Q X /Q Y state coupling is analysed from data obtained from site-selective excitation spectra, revealing pronounced matrix and site effects. From this analysis, the splitting of the Q X and Q Y states has been determined more accurately than in any previous attempts.

The absorption spectra of thin film samples, formed by the codeposition of sodium vapor with the rare gases have long been known to consist of complex structures in the region of the atomic sodium "yellow-doublet" lines. The photophysical characteristics of the associated luminescence (excitation/emission) spectra, indicate strong interaction between the excited P state Na atom and the rare gases (Ar, Kr, and Xe) used as host solids. This system is reinvestigated with new experimental spectroscopic results and molecular dynamics (MD) calculations. The so-called "violet" site in Ar and Kr has been produced by laser excitation of thermally deposited samples. The simulation of the "spray-on" deposition of thin films enables identification of tetravacancy (tv) sites of isolation for ground-state atomic sodium in Ar while in Kr this site is found in addition to single vacancy (sv) occupancy. Various cubic symmetry sites were taken into account to simulate absorption and emission spectra using accurate interaction potentials for the Na · RG diatomics. The wellknown 3-fold splitting in absorption, attributed to the Jahn-Teller effect, was very well reproduced but the simulated spectra for all the sites considered are located in the low energy region of the experimental bands. The evolution of the excited state Na atom is followed revealing the nature and symmetry of the sites that are transiently occupied. Consistent with the large Stokes shift observed experimentally, there is an extensive rearrangement of the lattice in the excited state with respect to the ground state. Combining all the experimental and theoretical information, an assignment of experimental violet, blue, and red absorption features is established involving single vacancy, tetravacancy, and hexavacancy sites, respectively, in Ar and Kr.

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HCN is a molecule of astrochemical interest. In this study, it was produced in cryogenic Ar and Kr matrices from UV-photolyzed diacetylene/cyanodiacetylene mixtures. Its strong phosphorescence was discovered and served for the identification of the compound. Vibrationally resolved phosphorescence excitation spectra gave insight into excited singlet electronic states. Two electronic systems were observed around 26 000-34 000 cm and 35 000-50 000 cm. Energies of the second excited singlet and the lowest triplet state were derived from analysis of these systems. Vibrational and electronic spectroscopic features were assigned with the assistance of density functional theory calculations. Some trends concerning the electronic spectroscopy of HCN family molecules are presented.

UV laser irradiations of cryogenic solid argon matrices doped with a mixture of acetylene and cyanodiacetylene (HC5N) resulted in the formation of a longer carbon-nitrogen chain, cyanotriacetylene (HC7N). The identification of this species was accomplished based on IR vibrational spectroscopy (including the study of isotopically labeled compounds), on electronic luminescence spectroscopy, and on theoretical predictions. Additionally, IR absorption bands recognized as due to HC7N were detected in photolysed Ar matrices doped with a cyanoacetylene/diacetylene mixture; this assignment was confirmed with the mass spectrometry of gases released upon the warm-up of the sample.

UV laser excitation of cryogenic solids doped with cyanoethyne, HC(3)N, led to an in situ creation of longer carbon-nitrogen chains, namely HC(5)N, C(4)N(2), and C(6)N(2), heralded by their strong visible luminescence. HC(5)N and C(4)N(2) molecules can form, most probably, within HC(3)N aggregates linked by hydrogen bonds, while the reaction occurring between two isolated, photochemically created C(3)N radicals yields C(6)N(2). This latter species, dicyanobutadiyne, is easily detected in Ar, Kr, N(2), as well as in parahydrogen solids. The C(6)N(2) phosphorescence is identified here for the first time. The reported carbon chain coupling reactions in rigid environments are of interest for astrochemistry of interstellar ices.