Christopher J. Gruenloh

Resonant ion-dip infrared spectroscopy of the S4 and D2d water octamers in benzene-(water)8 and benzene2-(water)8

The techniques of resonant two-photon ionization (R2PI), UV–UV (ultraviolet) hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopies have been employed along with density functional theory (DFT) calculations to assign and characterize the hydrogen-bonding topologies of two isomers each of the benzene-(water)8 and (benzene)2(water)8 gas-phase clusters. The BW8 isomers (B=benzene, W=water) have R2PI spectra which are nearly identical to one another, but shifted by about 5 cm−1 from one another. This difference is sufficient to enable interference-free RIDIR spectra to be recorded. As with smaller BWn clusters, the BW8 clusters fragment following photoionization by loss of either one or two water molecules. The OH stretch IR spectra of the two BW8 isomers bear a close resemblance to one another, but differ most noticeably in the double-donor OH stretch transitions near 3550 cm−1. Comparison to DFT calculated minimum energy structures, vibrational frequencies, and infrared intensities leads to an a...

Resonant ion-dip infrared spectroscopy of benzene–(water)9: Expanding the cube

The techniques of resonant two-photon ionization (R2PI), UV-UV hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopy have been employed along with density functional theory (DFT) calculations to characterize the hydrogen-bonding topologies of three isomers of benzene–(water)9. Isomers I and II, with R2PI transitions shifted, respectively, by +77 and +63 cm−1 from the benzene monomer, have similar intensities in the R2PI spectrum. The signal from the third isomer (isomer III, shifted +60 cm−1) is present at about one-fourth the intensity of the other two. The experimental RIDIR spectrum of isomer I bears a strong resemblance to the spectrum of the benzene–(water)8 D2d-symmetry cubic structure identified in earlier work, but possessing an extra single-donor transition associated with the ninth water molecule. Using the S4 and D2d symmetry forms of the water octamer as base structures to which the ninth water molecule can be added, a total of nine “expanded-cube” structures are identified for W9 a...

The infrared spectroscopy of hydrogen-bonded bridges: 2-pyridone-(water)n and 2-hydroxypyridine-(water)n clusters, n=1,2

The water-containing clusters of the two tautomers 2-hydroxypyridine (2HP) and 2-pyridone (2PYR) are studied in the hydride stretch region of the infrared using the techniques of resonant ion-dip infrared spectroscopy (RIDIRS) and fluorescence-dip infrared spectroscopy (FDIRS). The results on 2PYR-(water)n build on previous high-resolution ultraviolet spectroscopy [Held and Pratt, J. Am. Chem. Soc. 115, 9708 (1993)] on the n=1,2 clusters and the infrared depletion spectra of Matsuda et al. [J. Chem. Phys. 110, 8397 (1999)] on the n=1 cluster. The 2PYR-W2 FDIR spectrum reflects the consequences of extending and strengthening the H-bonded bridge between N–H and C=O sites in 2PYR. The spectrum shows evidence of strong coupling along the bridge, both in the form of the hydride stretch normal modes and in the breadth of the observed infrared transitions. RIDIR spectra of the 2HP-Wn clusters are compared with those of 2PYR-Wn in order to assess the spectroscopic consequences of forming the analogous water bridg...

RESONANT ION-DIP INFRARED SPECTROSCOPY OF TERNARY BENZENE-(WATER)N(METHANOL)M HYDROGEN-BONDED CLUSTERS

Resonant two-photon ionization, IR−UV hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopies have been employed along with density functional theory (DFT) calculations to assign and characterize the hydrogen-bonded topologies and structures of eight benzene−(H2O)n(CH3OH)m, cluster isomers (hereafter shortened to BWnMm) with n + m ≤ 4. The O−H stretch infrared fundamentals are used to determine the H-bonding topology of the clusters. However, in several cases, the O−H stretch spectrum leaves an ambiguity regarding the position of the methanols within the structure. In these cases, the methyl CH stretch region serves as a secondary probe capable of distinguishing among the various possibilities. For n + m = 2, a single BWM isomer is observed with OH stretch fundamentals at 3508, 3606, and 3718 cm-1. A comparison of the methyl CH stretch transitions of BWM and BM2 reveals that the methanol in BWM accepts a H-bond from water and forms a π H-bond with benzene. The n + m = 3 results show the subtle ...

Resonant ion-dip infrared spectroscopy of benzene–(water)n–(methanol)m clusters with n+m=4, 5

Abstract Resonant two-photon ionization and resonant ion-dip infrared (RIDIR) spectra of benzene–(water) n –(methanol) m clusters (hereafter shortened to BW n M m ) have been recorded for a total of seven clusters with n + m =4 and 5. The infrared spectra in the OH and CH stretch regions show absorptions characteristic of H-bonded W n M m clusters which are bound to benzene by a π H-bond involving a dangling OH on the W n M m sub-unit. Density functional theory (DFT) calculations identify a number of conformational isomers in the n + m =4 series which meet the general criteria imposed by the experimental spectra. The structures, binding energies, harmonic vibrational frequencies, and infrared intensities for these isomers have been calculated for comparison with experiment. Based on the calculations, tentative assignments of several of the observed species are given. The calculations uncover the fact that complexation of benzene to the cyclic water tetramer imposes much the same perturbations on the cycle as substitution of methanol for water. In particular, the single-donor OH stretch spectra of W n M m and BW n +1 M m −1 are calculated to be virtually identical to one another. The comparison of experiment and theory for this series of cyclic structures is used to assess the strengths and limitations of the calculations at the DFT Becke3LYP/6-31+G * level of theory.

The ultraviolet and infrared spectroscopy of (benzene)2-(CH3OH)3 isomeric clusters

Abstract A combination of resonant two-photon ionization (R2PI), resonant ion-dip infrared (RIDIR) and infrared-ultraviolet (IR-UV) hole-burning spectroscopies has been used to distinguish, assign, and spectroscopically characterize an otherwise complicated, overlapping set of transitions which all appear in the benzene-(CH3OH)3+ mass channel (m/e = 174) in a one-color resonant two-photon ionization spectrum. Several of the previously unassigned transitions are here assigned to two conformational isomers of (benzene)2-(CH3OH)3 clusters.