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Vibrational energy relaxation (VER) of the Fermi polyads in the CH stretching vibration of the benzene dimer (Bz2) and trimer (Bz3) has been investigated by picosecond (ps) time-resolved IR-UV pump-probe spectroscopy in a supersonic beam. The vibrational bands in the 3000-3100 cm-1 region were excited by a ps IR pulse and the time evolutions at the pumped and redistributed (bath) levels were probed by resonance enhanced multiphoton ionization with a ps UV pulse. For Bz2, a site-selective excitation in the T-shaped structure was achieved by using the isotope-substituted heterodimer hd, where h = C6H6 and d = C6D6, and its result was compared with that of hh homodimer. In the hd heterodimer, the two isomers, h(stem)d(top) and h(top)d(stem), show remarkable site-dependence of the lifetime of intracluster vibrational energy redistribution (IVR); the lifetime of the Stem site [h(stem)d(top), 140-170 ps] is ∼2.5 times shorter than that of the Top site [h(top)d(stem), 370-400 ps]. In the transient UV spectra, a broad electronic transition due to the bath modes emerges and gradually decays with a nanosecond time scale. The broad transition shows different time profile depending on UV frequency monitored. These time profiles are described by a three-step VER model involving IVR and vibrational predissociation: initial → bath1(intramolecular) → bath2(intermolecular) → fragments. This model also describes well the observed time profile of the Bz fragment. The hh homodimer shows the stepwise VER process with time constants similar to those of the hd dimer, suggesting that the excitation-exchange coupling of the vibrations between the two sites is very weak. Bz3 also exhibited the stepwise VER process, though each step is faster than Bz2. [ABSTRACT FROM AUTHOR]

IR photodissociation (IRPD) spectra of (N2O)2+•Ar and (N2O)n+ with n=3–8 are measured in the 1000–2300 cm-1 region. The (N2O)2+•Ar ion shows an IRPD band at 1154 cm-1, which can be assigned to the out-of-phase combination of the ν1 vibrations of the N2O components in the N4O2+ ion; the positive charge is delocalized over the two N2O molecules. The geometry optimization and the vibrational analysis at the B3LYP/6-311+G* level show that the N4O2+ ion has a C2h structure with the oxygen ends of the N2O components bonded to each other. The IRPD spectra of the (N2O)n+(n=3–8) ions show three prominent bands at ∼1170, ∼1275, and ∼2235 cm-1. The intensity of the ∼1170 cm-1 band relative to that of the other bands decreases with increasing the cluster size. Therefore, the ∼1170 cm-1 band is ascribed to the N4O2+ dimer ion core and the ∼1275 and ∼2235 cm-1 bands are assigned to the ν1 and ν3 vibrations of solvent N2O molecules, respectively. Since the band of the N4O2+ ion core is located at almost the same position for all the (N2O)n+(n=2–8) clusters, the C2h structure of the dimer ion core does not change so largely by the solvation of N2O molecules, which is quite contrastive to the isoelectronic (CO2)n+ case. [ABSTRACT FROM AUTHOR]

Infrared photodissociation (IRPD) spectra of [H2O•(CO2)n]+ and [CH3OH•(CO2)n]+ (n=1–7) are measured in the 1100–3800 cm-1 region. At the same time, the solvation characteristics in the clusters are investigated theoretically; the geometry optimization and the vibrational analysis are carried out for the [H2O•(CO2)n]+ (n=1–4) and the [CH3OH•(CO2)n]+ (n=1–3) ions at the MP2/6-31+G* level of theory. The IRPD spectrum of the [H2O•(CO2)1]+ ion shows the free OH and the hydrogen-bonded OH stretching bands of the H2O+ ion core and the antisymmetric CO stretching band of the solvent CO2 molecule, indicating that the solvent CO2 molecule is preferentially solvated to the H2O+ ion core via the O–H•••OCO hydrogen bond. In [H2O•(CO2)2]+, the free OH stretching band is not observed; both of the OH groups of the H2O+ ion core are hydrogen bonded to the solvent CO2 molecules. Spectral features of the IRPD spectra of [H2O•(CO2)n]+ (n=3–7) suggest that the third and the fourth CO2 molecules are bound to the oxygen atom of the H2O+ ion core, and that the first solvation shell of the H2O+ ion core becomes filled with four CO2 molecules. All the IRPD spectra of the [CH3OH•(CO2)n]+ (n=1–7) ions display the hydrogen-bonded OH stretching band of the CH3OH+ ion core, meaning that the solvent CO2 molecule is preferentially bonded to the OH group of the CH3OH+ ion core, similar to the case of [H2O•(CO2)n]+. Quantum chemical calculations for the [CH3OH•(CO2)1–3]+ ions demonstrate that the second and the third solvent CO2 molecules are bonded to the oxygen atom of the CH3OH+ ion core. [ABSTRACT FROM AUTHOR]

Infrared photodissociation (IRPD) spectra of carbon dioxide cluster ions, (CO2)n+ with n=3–8, are measured in the 1000–3800 cm–1 region. IR bands assignable to solvent CO2 molecules are observed at positions close to the vibrational frequencies of neutral CO2 [1290 and 1400 cm–1 (ν1 and 2ν2), 2350 cm–1 (ν3), and 3610 and 3713 cm–1 (ν1+ν3 and 2ν2+ν3)]. The ion core in (CO2)n+ shows several IR bands in the 1200–1350, 2100–2200, and 3250–3500 cm–1 regions. On the basis of previous IR studies in solid Ne and quantum chemical calculations, these bands are ascribed to the C2O4+ ion, which has a semicovalent bond between the CO2 components. The number of the bands and the bandwidth of the IRPD spectra drastically change with an increase in the cluster size up to n=6, which is ascribed to the symmetry change of (CO2)n+ by the solvation of CO2 molecules and a full occupation of the first solvation shell at n=6. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectra of (CS2)n+ and (CS2)n- with n=3–10 are measured in the 1100–2000 cm-1 region. All the (CS2)n+ clusters exhibit three bands at ∼1410, ∼1490, and ∼1540 cm-1. The intensity of the 1540 cm-1 band relative to those of the other bands increases with increasing the cluster size, indicating that the band at 1540 cm-1 is assignable to the antisymmetric CS stretching vibration of solvent CS2 molecules in the clusters. On the basis of density functional theory calculations, the 1410 and 1490 cm-1 bands of (CS2)n+ are assigned to CS stretching vibrations of the C2S4+ cation core with a C2 form. The (CS2)n- clusters show two bands at around 1215 and 1530 cm-1. Similar to the case of cation clusters, the latter band is ascribed to the antisymmetric CS stretching vibration of solvent CS2 molecules. Vibrational frequency analysis of CS2- and C2S4- suggests that the 1215 cm-1 band is attributed to the antisymmetric CS stretching vibration of the CS2- anion core with a C2v structure. [ABSTRACT FROM AUTHOR]

The encapsulation of neutral guest has been studied for calix[4]arene (C4A) by forming van der Waals clusters with Ar and Ne in supersonic jets. The electronic transitions of these clusters suggest that the first Ar (Ne) is encapsulated inside the C4A cavity, while the next atoms are bound outside. [ABSTRACT FROM AUTHOR]

The cis↔trans isomerization reaction has been carried out for 2-naphthol and its hydrogen (H) bonded clusters by infrared (IR) laser in the electronic excited state (S1) in supersonic jets. A specific isomer in the jet was pumped to the X–H stretching vibration in the S1 state, where X refers to C, O, or N atom, by using a stepwise UV-IR excitation, and the dispersed emission spectra of the excited species or generated fragments were observed. It was found that the isomerization occurs only in the H-bonded clusters but a bare molecule does not exhibit the isomerization in the examined energy region of Ev≤3610 cm-1, indicating a reduction of the isomerization barrier height upon the H bonding. The relative yield of the isomerization was observed as a function of internal energy. The isomerization yield was found to be very high at the low IR frequency excitation, and was rapidly reduced with the IR frequency due to the competition of the dissociation of the H bond within the isomer. Density-functional theory (DFT) and time-dependent DFT calculations were performed for estimating the barrier height of the isomerization for bare 2-naphthol and its cluster for electronic ground and excited states. The calculation showed that the isomerization barrier height is highly dependent on the electronic states. However, the reduction of the height upon the hydrogen bonding was not suggested at the level of our calculation. [ABSTRACT FROM AUTHOR]

Intramolecular vibrational energy redistribution (IVR) of the NH2 symmetric and asymmetric stretching vibrations of jet-cooled aniline has been investigated by picosecond time-resolved IR-UV pump-probe spectroscopy. A picosecond IR laser pulse excited the NH2 symmetric or asymmetric stretching vibration of aniline in the electronic ground state and the subsequent time evolutions of the excited level as well as redistributed levels were observed by a picosecond UV pulse. The IVR lifetimes for symmetric and asymmetric stretches were obtained to be 18 and 34 ps, respectively. In addition, we obtained the direct evidence that IVR proceeds via two-step bath states; that is, the NH2 stretch energy first flows into the doorway state and the energy is further dissipated into dense bath states. The rate constants of the second step were estimated to be comparable to or slower than those of the first step IVR. The relaxation behavior was compared with that of IVR of the OH stretching vibration of phenol [Y. Yamada, T. Ebata, M. Kayano, and M. Mikami J. Chem. Phys. 120, 7400 (2004)]. We found that the second step IVR process of aniline is much slower than that of phenol, suggesting a large difference of the “doorway state↔the dense bath states” anharmonic coupling strength between the two molecules. We also observed IVR of the CH stretching vibrations, which showed much faster IVR behavior than that of the NH2 stretches. The fast relaxation is described by the interference effect, which is caused by the coherent excitation of the quasistationary states. [ABSTRACT FROM AUTHOR]

A picosecond time-resolved IR-UV pump–probe spectroscopic study was carried out for the intramolecular vibrational energy redistribution of the OH/OD stretching vibration of isolated phenol and its isotopomers in supersonic beams. The time evolution due to IVR showed a significant isotope effect; the OH stretch vibration showed a single exponential decay and its lifetime is greatly lengthened upon the deuterium substitution of the CH group. The OD stretch vibration exhibited prominent quantum beats. Especially, in phenol-d1 (C6H5OD), the electronic transitions from the doorway states were clearly observed. They exhibited an out-of-phase quantum beat with respect to that of the OD stretch level and disappeared due to further IVR to the dense bath states. The transient spectra as well as the time evolution clearly evidenced the tier-model of the description of intramolecular vibrational energy redistribution. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A picosecond time-resolved IR–UV pump–probe spectroscopic study has been carried out for investigating the intracluster vibrational energy redistribution (IVR) and subsequent dissociation of hydrogen-bonded clusters of phenol (C6H5OH) and partially deuterated phenol (C6D5OH, phenol-d5) with various solvent molecules. The H-bonded OH stretching vibration was pumped by a picosecond IR pulse, and the transient S1–S0 UV spectra from the pumped level as well as the redistributed levels were observed with a picosecond UV laser. Two types of hydrogen-bonded clusters were investigated with respect to the effect of the H-bonding strength on the energy flow process: the first is of a strong “σ-type H-bond” such as phenol-(dimethyl ether)n=1 and phenol dimer, and the second is phenol-(ethylene)n=1 having a weak “π-type H-bond.” It was found that the population of the IR-pumped OH level exhibits a single-exponential decay, whose rate increases with the H-bond strength. On the other hand, the transient UV spectrum due to the redistributed levels showed a different time evolutions at different monitoring UV frequency. From an analysis of the time profiles of the transient UV spectra, the following three-step scheme has been proposed for describing the energy flow starting from the IVR of the initially excited H-bonded OH stretching level to the dissociation of the H bond. (1) The intramolecular vibrational energy redistribution takes place within the phenolic site, preparing a hot phenol. (2) The energy flows from the hot phenol to the intermolecular vibrational modes of the cluster. (3) Finally, the hydrogen bond dissociates. Among the three steps, the rate constant of the first step was strongly dependent on the H-bond strength, while the rate constants of the other two steps were almost independent of the H-bond strength. For the dissociation of the hydrogen bond, the observed rate constants were compared with those calculated by the Rice, Ramsperger, Kassel, and Marcus model. The result suggests that dissociation of the hydrogen bond takes place much faster than complete energy randomization within the clusters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intramolecular vibrational energy redistribution (IVR) of the OH stretching vibration of jet-cooled phenol-h6 (C6H5OH) and phenol-d5 (C6D5OH) in the electronic ground state has been investigated by picosecond time-resolved IR–UV pump–probe spectroscopy. The OH stretching vibration of phenol was excited with a picosecond IR laser pulse, and the subsequent temporal evolutions of the initially excited level and the redistributed ones due to the IVR were observed by multiphoton ionization detection with a picosecond UV pulse. The IVR lifetime for the OH stretch vibration of phenol-h6 was determined to be 14 ps, while that of the OH stretch for phenol-d5 was found to be 80 ps. This remarkable change of the IVR rate constant upon the dueteration of the CH groups strongly suggests that the “doorway states” for the IVR from the OH level would be the vibrational states involving the CH stretching modes. We also investigated the IVR rate of the CH stretching vibration for phenol-h6. It was found that the IVR lifetime of the CH stretch is less than 5 ps. The fast IVR is described by the strong anharmonic resonance of the CH stretch with many other combinations or overtone bands. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An infrared laser induced cis↔trans isomerization has been investigated for 2-naphthol and its hydrogen(H)-bonded cluster with NH[SUB3] in the S[SUB1] electronic state by UV-IR double resonance excitation in a supersonic jet. A specific isomer was pumped to a X-H (X = O, C or N) stretching vibration in S[SUB1] by a sequential UV-IR two-photon excitation, and the resultant product species were analyzed by dispersing their fluorescence. It was found that the IR excitation induces the isomerization for the H-bonded cluster with the excitation less than 3000 cm[SUP-1], while no isomerization was found to occur for bare 2NpOH even with an input energy of 3610 cm[SUP-1]. The substantial reduction of the isomerization barrier height represents evidence of the catalytic nature of H-bonding in the conformational isomerization. It was also found that the isomerization efficiency is very high at low IR frequency and exhibits a marked IR frequency dependence. [ABSTRACT FROM AUTHOR]

Continuing with our earlier communication on the dihydrogen bonded phenol-borane-dimethylamine complex [J. Chem. Phys. 113, 9885 (2000)], we report here, the realistic structure of the said complex calculated using density functional theory at B3LYP/6-31 + + G(d,p) level. The agreement between the experimental and calculated vibrational spectrum for both the N-H and O-H stretching vibrations along with the low-frequency vibrations that appear in combination with O-H stretching, provides the basis for structural assignment. Analysis of the fate of B-H bonds and B-H stretching vibrations upon formation of dihydrogen bond reveals an anomalous behavior of average bond strengthening. [ABSTRACT FROM AUTHOR]

The S[sub 1]-S[sub 0] electronic spectra, and the vibrational spectra of jet-cooled 2-pyridone (2PY) and its hydrogen bonded clusters, 2PY-H[sub 2]O and 2PY dimer, have been investigated by population labeling and various double-resonant vibrational spectroscopies. For bare 2PY, the S[sub 1]-S[sub 0] spectrum was measured by laser-induced fluorescence and population labeling spectroscopy. In addition, IR and Raman spectra of the NH stretching vibration were observed in S[sub 0] and S[sub 1]. The results led to the conclusion that 2PY has two close lying electronic states in the S[sub 1] region, whose structures are slightly different with respect to the NH group. It was also found that the NH stretching frequency becomes smaller in S[sub 1] than in S[sub 0], indicating that the NH bond strength of 2PY becomes weaker in S[sub 1]. The effect of the electronic excitation on the hydrogen bond strength has also been investigated by measuring the NH and OH stretching vibrations of the hydrogen bonded clusters in the two electronic states, and it was found that the hydrogen-bond strength is weaker in S[sub 1] than in S[sub 0]. For 2PY dimer, the IR and the Raman spectra of the NH stretching bands showed a clear intensity alternation, confirming its C[sub 2h] symmetric structure. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the structures of the benzyl alcohol and its hydrogen-bonded clusters with water using infrared-ultraviolet double resonance vibrational spectroscopy along with ab initio molecular-orbital calculations. Characteristic shifts of the hydroxide stretching vibrations of the benzyl alcohol site as well as the water sites.

Studies the vibrational spectroscopy of jet-cooled benzonitrile and its clusters by simulated Raman-ultraviolet and infrared-ultraviolet double resonance methods. Stretching vibrations for each species; Cluster structures determined by comparing the observed spectra; Size-dependent transmutation of the hydrogen-bond structure.

Focuses on the vibrational spectroscopy of the key functional vibrations of 2-pyridone and its hydrogen-bonded clusters with water, methanol, dimethylether, as well as its dimer, using infrared-ultraviolet and stimulated Raman-UV double resonance methods. Appropriateness of the ring-type hydrogen-bonded structure for the cluster with water or methanol.

Discusses the application of an infrared spectroscopic technique for jet-cooled molecular cations to observe intramolecular hydrogen bonds in substituted phenol ions. Measurement of vibrational transitions of an ion core of high Rydberg states by detecting molecular ions prepared through vibrational autoionization.

OH and CH stretching vibrations of bare phenol, phenol-(H2O)n clusters (n=1–4), and partially deuterated clusters in the S0 state were observed by using IR–UV double resonance and stimulated Raman-UV double resonance spectroscopies. Characteristic spectral features of the OH stretching vibrations of the phenol as well as of the H2O sites were observed, which are directly related to their structures. The cluster structures were investigated by comparing the observed spectra with the calculated ones obtained by the ab initio molecular orbital calculation with (self-consistent field) SCF 6-31G and SCF 6-31G* basis sets given by Watanabe and Iwata. It was found that for the clusters with n≥2, the isomer of ring form hydrogen-bonded structure is most stable and the simulated IR spectra based on the calculated structure showed good agreements with the observed ones. For a particular cluster, which was assigned as an isomer of the n=4 cluster, an anomalous IR spectrum was observed. Two forms of the isomer are proposed with respect to the structure of water moiety: (1) an ‘‘ice’’ structure and (2) an ‘‘ion-pair’’ structure. The relative IR absorption cross sections of each bands were also investigated for the clusters with n=1 to 4. It was found that the IR absorption cross section of the phenolic OH stretching vibration of the n=1 cluster increases by a factor of 6 compared to that of bare phenol and it further increases with the cluster size. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In a series of spectroscopic work of the Rydberg states of CO, we present the rotational analysis of the v=0 and 1 levels of the singlet ns, np, nd and nf-Rydberg states (n=4–7). The spectra were measured by ion-dip spectroscopy with triple resonance excitation via the 3sσ:B 1Σ+ or the 3pσ:C 1Σ+ state. All the spectra were rotationally well resolved and the term value, quantum defect and the rotational constant were obtained for each state. Through the analysis of the rotational structure, the coupling between the Rydberg electron and the ion core has been investigated. For the np-Rydberg states, a switching from Hund’s case (b) to (d) was clearly observed with the increase of n. A significant perturbation was observed in the 6pπ 1Π and 7pπ 1Π states and it is suggested that these states are perturbed by the state with the same symmetry. For the nf-Rydberg states, the observed electronic energy was well analyzed by the long range force model and the precise ionization potential was obtained. The Rydbergvalence and inter-Rydberg states interactions were also investigated. For the ns-Rydberg states, the interaction matrix element with the repulsive state was estimated from the measurement of linewidth of the rotational levels. The potential curve of the repulsive state to which ns-Rydberg states predissociate was also determined. Selective predissociation was found for the e-symmetry levels both in the v=0 and 1 levels of the nf-Rydberg state. A strong interaction between the v=0 levels of the 6d- and 7s-Rydberg states was observed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rotationally resolved spectra of the 5s–7s, 5p–7p, 5d, 6d, and 4f–6f Rydberg states (v=1) of jet cooled CO have been measured by ion-dip spectroscopy with triple resonance excitation via the 3sσ B 1Σ+(v=1) state. The dip spectra due to the high Rydberg (v=1)←B 1Σ+(v=1) transition revealed the states most of which have not been observed by other spectroscopy. By the rotational analysis of the dip spectra, electronic term values, quantum defects, and rotational constants were obtained. For the np Rydberg states, the change of the angular momentum coupling between the p Rydberg electron and the CO+ core was clearly observed as a function of the principal quantum number, n, indicating a transition from Hund’s case (b) to Hund’s case (d). It was found that the rotational constant of the nsσ state increases with n, while that of the ndσ state decreases. The changes in the rotational constants were interpreted by the mixing between the nsσ state and the (n-1)dσ state and the mixing coefficients for those states were determined. For the 4f, 5f, and 6f Rydberg states, only the rotational levels belonging to e-symmetry were observed in the dip spectrum. It indicates the selective predissociation through the low lying D’ 1Σ+ state. [ABSTRACT FROM AUTHOR]

A detailed analysis of the rotational structure of high Rydberg states of CO converging to the ionic state is presented. These states were pumped from the 3sσB 1Σ+ state using triple resonant multiphoton excitation. The observed states were n=8∼10 of the s-, p-, d-, and f-Rydberg states in the vibrational levels with v=1. The observed spectra were rotationally well resolved and the term values, the quantum defects, and the rotational constants were obtained for these states. p- and f-Rydberg states were described by the Hund’s coupling case (d). On the other hand, only the σ component was observed for the d-Rydberg states and its linewidth was very broad. For the nf-Rydberg state, the long range force model was used to obtain the ionization potential of CO(v=1), the polarizability and the quadrupole moment of the CO+ core. The mixing among Rydberg states seems to be large, as suggested by anomalous values of the rotational constants for several states. In particular, in the nf-Rydberg states, a rotational branch that should not appear for a pure Rydberg state was observed, and was explained by mixing with nearby (n+1)s-Rydberg states. [ABSTRACT FROM AUTHOR]

The two-color double resonance multiphoton ionization and fluorescence dip spectra due to the transitions from various rotational levels of the D 2Σ+ (v=1) state of NO to its high Rydberg states have been measured. Coherent vacuum ultraviolet (VUV) light generated by four wave mixing in Hg was used in the first excitation step. The ns(v=1) and nd(v=1) Rydberg series with 7≤n≤32 were observed. The rotational analysis for the d Rydberg series indicates that only the Π- component appears in the MPI spectra. A large dependence of the rotational constant upon n for the nd Π- Rydberg states was found and interpreted in terms of dΠ-–dΔ- mixing. An anomalous intensity distribution was also found for the rotational branches of the ns Rydberg states in the transition from the D 2Σ+ state. The anomaly is explained by the ns–(n-1)d mixing. [ABSTRACT FROM AUTHOR]

Formic acid monomer was excited to the S1(nπ*) region from 220 to 250 nm. The generated OH fragment was studied by the fluorescence excitation spectrum of the A 2∑+–X 2∏ transition under a high resolution and with different laser polarization geometries. The internal state distribution, translational energy and angular distribution of the OH fragment were determined by the observed results. No vibrational excitation was observed ( fv<0.009) for the OH fragment. Though the rotational excitation is also low ( fr<0.06), the fraction increases with the dissociation energy. The spin–orbit components are roughly in equilibrium. The degree of alignment of the OH fragment is very small and its π-lobe lies preferentially in the plane of rotation. The translational energy of the OH fragment is relatively high ( ft∼0.34) but the Doppler line shape does not show any clear sin2 θ or cos2 θ dependence. These results indicate that the S1 state dissociates directly through a pyramidal structure or that the dissociation is not direct dissociation but is predissociation. Compared to the OH fragment, the HCO fragment is thought to be internally very excited ( fint∼0.3) as a result of the character of S1(nπ*) state. [ABSTRACT FROM AUTHOR]

Laser induced fluorescence (LIF) detection has been applied to measure the rotational distribution of the N+2 ion produced by double resonant multiphoton ionization of the N2 molecule. By analysis of the LIF spectra of the generated N+2 ion, the rotational propensity rules of the photoionization of N2 have been determined, which agree with theoretical prediction. The observed rotational intensity distribution shows relatively good agreement with the calculated result. Rotational relaxation of the N+2 ions by N2 collision has also been measured. The rotational relaxation rate constant is almost equal to that of the vibrational relaxation and the selection rule ‘‘symmetric’’ (+)↔‘‘symmetric’’(+) has been found to be obeyed. [ABSTRACT FROM AUTHOR]

The effects of vibrational excitation of the ammonia ν2 inversion mode on the reaction of NH+3(X,v=0 to 9) with methane have been measured in a tandem quadrupole mass spectrometer over the center-of-mass collision energy range 1.5 to 10 eV. The hydrogen abstraction channel is enhanced by nearly a factor of 2 at nine quanta of vibrational energy relative to the v=0 level of the ion. Added vibration in the ammonia ion umbrella-bending mode facilitates the transition to the NH+4 product ion geometry. Protonated methylamine is formed at lower kinetic energies by attack of the ion at the methane carbon center, but with increasing vibrational excitation of the ammonia ion, the protonated methylamine decomposes by 1,2-elimination of molecular hydrogen and by C–N bond scission. [ABSTRACT FROM AUTHOR]

Examines the hydrogen-bond structures of 2-naphthol-(H[sub 2]O)n clusters by infrared-ultraviolet double resonance spectroscopy. Identification of cis- and trans-isomers of 2-naphthol; Measurement of 2-naphthol under low water vapor pressure; Similarities between two rotamers of 2-naphthol-(H[sub 2]O)n in vibrational structure.

Examines the Rydberg states of carbon monoxide by monitoring the fragment atoms generated by predissociation. Measurement of the photofragment atoms produced by the predissociation process; Determination of the molecular constants of the Rydberg states; Comparison of predissociation rates between the triplet and singlet channel.

Studies the predissociation mechanism of the C state of jet-cooled silicon dioxide. Degenerate four-wave mixing spectrum; Relative fluorescence quantum yields of various vibronic bands; Initiation of the nonradiative process of the state; Level wherein predissociation occurred.

Infrared spectra of jet-cooled tropolone-(H[SUB2]O)[SUBn] (n = 1-3) and tropolone-(CH[SUB3]OH)[SUBn] (n = 1 and 2) clusters were observed in the OH stretching region by using infrared-ultraviolet double resonance techniques. Size separated electronic spectra of these clusters were also observed with hole-burning spectroscopy in which the infrared laser was used as hole light. Both the infrared and hole-burning spectra of the tropolone-methanol clusters were found to be quite similar to those of the corresponding tropolone-water clusters, indicating that a similar structure is expected for both the clusters. Structure of the n51 and 2 clusters of tropolone-water and -methanol is discussed. The infrared (IR) spectra suggest that the intramolecular hydrogen bond of tropolone OH is not destroyed in tropolone-(H[SUB2]O)[SUBn] (n&les;2) and -CH[SUB3]OH, while the intermolecular hydrogen bond dominates in tropolone-(H[SUB2]O)[SUB3] and -(CH[SUB3]OH)[SUB2]. The transformation of the intramolecular to intermolecular hydrogen bond induced by the solvation is also discussed. [ABSTRACT FROM AUTHOR]

Resonance enhanced multiphoton ionization has been applied to the production of vibrationally state-selected ion beams. Ammonia ions are selectively formed with a specific number of vibrational quanta in the ν2 umbrella bending mode. The effect of vibrational excitation of this mode on the reaction of NH+3(X, v=0 to 9) with D2 is examined over the 0.5 to 10 eV center-of-mass kinetic energy range in a tandem quadrupole mass spectrometer. Under these conditions, (1) abstraction of a D atom to form NH3D+ is the dominant reaction channel, (2) NH3D+ having sufficient internal energy may decompose to yield NH2D+ and this decomposition process is enhanced by vibrational excitation of the NH+3 reagent, and (3) NH2D+ is also formed by direct hydrogen–deuterium exchange of NH+3 with D2, but this channel appears as a minor contribution which is insensitive to the vibrational excitation of the NH+3. A spectator stripping model is able to account for the ratio of NH2D+ to NH3D+ as a function of the NH+3 translational and vibrational energy. [ABSTRACT FROM AUTHOR]

Spectroscopic investigation of a dihydrogen bonded complex between phenol and borane-trimethylamine is reported here. Laser-induced fluorescence excitation, fluorescence detected infrared, and infrared-ultraviolet hole-burning spectroscopic studies were carried out in supersonic jets to investigate the complex formation between phenol and borane-trimethylamine. The redshift in the electronic transition and the low-frequency shift of the O-H stretching vibration established the proton donating ability of phenol in the complex. The experimental results together with the ab initio quantum mechanical calculations affirmed the formation of the dihydrogen bond in the complex. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The rate constants of intracluster vibrational energy redistribution (IVR) of benzonitrile-(CHCl[sub 3])[sub 1] for the 12[sub 1] (1000 cm[sup -1]), 1[sub 1] (760 cm[sup -1]), and 6a[sub 1] (460 cm[sup -1]) levels have been measured by time-resolved stimulated Raman-UV double resonance spectroscopy. It was found that the observed rate constants are independent of the energies but strongly dependent on the vibrational modes. In order to find a relationship between the structure and the IVR rate, structures of benzonitrile-(CHCl[sub 3])[sub n=1-3] have been determined based on the results of the Raman spectra and the high resolution S[sub 1]-S[sub 0] electronic spectra for the size-selected clusters, and ab initio MO calculations. The Raman spectra were observed for both CHCl[sub 3] and benzonitrile sites. It was found that the CH stretching vibration of the CHCl[sub 3] moiety showed a higher frequency shift in the clusters, whose magnitude depends on the binding site to benzonitrile. For the benzonitrile moiety, the Raman spectra of CH stretch (ν[sub 2]), CN stretch (ν[sub CN]), ring breathing (ν[sub 12] and ν[sub 1]), and CCC in-plane bending (ν[sub 6a]) vibrations were investigated. From those results, it was concluded that the clusters have the form such that the CH hydrogen of the first CHCl[sub 3] is hydrogen-bonded to the N end of the CN group, while second and third CHCl[sub 3] are hydrogen-bonded to the phenyl ring. The observed mode dependence of the IVR rate constants will be discussed based on the cluster structure and the vibrational motion. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Predissociation of Rydberg states of CO has been investigated by the C ([sup 3]P and [sup 1]D) and O([sup 3]P) photofragment measurements in the region of 103 000-114 000 cm[sup -1] (88-97 nm). The simulations of the rotational structures of np and nf Rydberg states were also carried out by using the l-uncoupling Hamiltonian model. The photofragment yield spectra were compared with the ion-dip spectra which correspond to the absorption spectra, indicating that all the Rydberg states, ns, np, nd, and nf converging to the X [sup 2]Σ[sup +] CO[sup +] ion, were subject to the predissociation. It was found that the lower member npπ and ndπ states exhibit two dissociation path ways, that is the C([sup 3]P)+O([sup 3]P) and the C([sup 1]D)+O([sup 3]P) channels. Especially, for the 4pπ L [sup 1]Π(v=0) state the two channels were found to be competitive with respect to parity as well as rotational quantum number J. At higher np series, such a parity and J-dependence of the predissociation disappeared, and the observed rotational structure was simulated very well by the model with no parity nor J dependence. For the ndσ states, the spectra of the 3dσ and 5dσ(v=0) states were diffuse, while the 4dσ(v=0) state showed a rotationally resolved photofragment yield spectrum. All the photofragment yield spectra of the nf(v=0) states exhibited sharp structures compared with those of other Rydberg states with a small l value. From a comparison between the photofragment yield spectrum and the ion-dip spectrum, it was found that the predissociation rate of the e-symmetry component is larger than that of the f-symmetry component. It was suggested that the e-symmetry levels predissociate through D[sup ′] [sup 1]Σ[sup +] valence states, while the f-symmetry levels predissociate through the 2 [sup 1]Π state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report here the formation of a gas phase complex bound by a dihydrogen bond between phenol and borane-dimethylamine in supersonic jets. Laser induced fluorescence excitation, fluorescence detected infrared, and IR-UV hole-burning spectroscopies were carried out to characterize the complex. Quantum chemical calculations were used to derive the structure of the complex, providing excellent agreement with the spectroscopic data. To the best of our knowledge, we for the first time established experimentally the formation of a dihydrogen bonded complex in the gas phase. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The CH stretching vibrations of the benzene-Ar, toluene-Ar, and ethylbenzene-Ar clusters prepared in jet expansion were observed in both the neutral and cationic ground states by using infrared-ultraviolet double resonance and infrared photodissociation spectroscopy, respectively. Vibrational frequencies for the in-plane modes of the clusters have been found to be practically the same as those of the corresponding bare molecules. The aromatic CH stretching vibrations showed high frequency shifts upon ionization, and their infrared absorption intensities remarkably decreased. The alkyl CH stretching vibrations were also significantly changed in both frequency and intensity upon ionization. Density functional calculations well reproduced the observed infrared spectra of the neutral and cationic states, and enhancement of hyperconjugation in the cationic state was pointed out. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A newly developed infrared spectroscopic technique, called autoionization-detected infrared (ADIR) spectroscopy, was applied for a study on hydroxyl-alkyl interactions in cresol and ethylphenol cations. In this technique, vibrational transitions in the ion core of high Rydberg states, which has almost the same vibrational structure as the corresponding bare molecular ion, are measured by detecting the vibrational autoionization signal. The OH stretching vibrations in the rotational isomers of the ortho-, meta-, and para-cresol cations and those of the ethylphenol cations were observed. Remarkable low-frequency shifts of the OH vibration were found only for the cis rotational isomers of the ortho-cresol and ortho-ethylphenol cations, whereas no such shift was found for all the other rotational and structural isomer cations. On the other hand, no remarkable shift of the OH stretch frequency was found for all the isomers in the neutral ground state. These results indicate that an intramolecular hydrogen bond is formed between the hydroxyl and alkyl groups in the cationic ground state of ortho-cresol and ortho-ethylphenol. The remarkable low-frequency shift of the OH vibration also indicates that the alkyl group acts as a proton acceptor in the hydrogen bond. This is a new type of intramolecular hydrogen bond, and the origin of such unconventional hydrogen bond in the cations is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]