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  • 1
    Electronic Resource
    Electronic Resource
    The first vibronically resolved measurement of correlated-product-state distributions in ultraviolet photodissociation: Ketene at 308 nm (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 611-614 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method is demonstrated which allows derivation of elements of the correlated-product-state distribution matrix in photodissociation. The method relies on quantum-state-specific, time-of-flight measurements, which were successfully carried out on CO produced in ketene photolysis at 308 nm. Such time-of-flight data exhibits well-defined peaks dictated by the CH2 internal state distribution occurring in coincidence with the chosen CO quantum state. For two rovibrational states of CO, peaks corresponding to the 1A1(0,0,0), 1A1(0,1,0), and 3B1 vibronic states of the CH2 fragment were clearly resolved. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469442
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  • 2
    Electronic Resource
    Electronic Resource
    The spin-forbidden a 4Π(ν=13–15) and b 4Σ−(ν=3)←X 2Π(ν=0) bands of nitric oxide: A new scheme for quantum state-specific high-resolution kinetic energy measurements (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7700-7707 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new scheme for performing high-resolution kinetic energy measurements on single quantum states of NO is described. Laser excitation of the a 4Π(ν=13–15) and b 4Σ−(ν=3)←X 2Π(ν=0) spin-forbidden bands has been used to produce NO a 4Π, either by direct excitation or after excitation to NO b 4Σ− followed by b→a emission. The sensitivity is compared to previous experiments on CO, employing the forbidden Cameron system. In the course of these experiments, three previously unknown vibronic levels of the a 4Π state were observed for which high precision molecular constants have been obtained. The derived molecular constants have been used to construct a chemically accurate RKR potential for the a 4Π state to within 0.2 eV of the dissociation limit. In addition, the electric dipole moments for the a 4Π(ν=13–14) levels have been determined. By comparing the experimental results with two ab initio calculations, the polarity of the dipole moment of the a 4Π state at equilibrium separation could be determined. A set of supplementary molecular beam laser-induced fluorescence studies on the b 4Σ−(ν=3)←X 2Π(ν=0) band were also carried out. These allowed the fluorescence lifetime of b 4Σ−(ν=3) state to be obtained under collision-free conditions and the electronic origin of the quartet manifold to be determined within 0.03 cm−1. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470292
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  • 3
    Electronic Resource
    Electronic Resource
    The C 3Π(v'=0–6)–X 3Π(v‘=0) transition in SiC (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2292-2298 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the measurement of seven rovibronic bands belonging to the C3Π(v'=0–6)-X3Π(v‘=0) transition in SiC. The molecules are produced by laser vaporization in combination with supersonic cooling and the transitions are detected using pulsed laser induced fluorescence spectroscopy. The vibrational and rotational structure of the C3Π state are determined. Radiative lifetimes vary from 2886 ns for v'=0 to 499 ns for v'=6. Dispersed fluorescence spectra from the excited vibrational levels to the ground state have been measured and the vibrational constants of the electronic ground state were obtained. Both the v' dependence of the radiative lifetime and observed anomalous intensity distributions in the fluorescence spectra are explained by an electronic transition moment function that varies with the internuclear distance. The results are compared with ab initio calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460988
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the singlet–triplet perturbations in the A˜ 1Au state of acetylene by high resolution ultraviolet spectroscopy (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 165-174 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser-induced fluorescence spectra of the 330 K10 and 340 K10 vibronic bands of the A˜ 1Au←X˜ 1Σ+g transition in acetylene have been recorded with a resolution of 18 MHz. Each rotational transition consists of a group of lines due to coupling of the electronically excited singlet state with isoenergetic triplet states. Using the standard deconvolution procedure the singlet–triplet coupling elements and the density of coupled triplet states are derived for rotational levels up to J=4 in both bands. From the density of coupled triplet states it is concluded that the A˜ 1Au state is perturbed by the T1 3B2 state. Magnetic field measurements have shown that the predissociation of acetylene in the 4ν3' vibrational level of the A˜ state is caused by a coupling via the T1 3B2 state with predissociating vibrational levels of the electronic ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466988
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  • 5
    Electronic Resource
    Electronic Resource
    The correlated product state distribution of ketene photodissociation at 308 nm (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7460-7474 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The correlated product state distribution for ketene photodissociation (CH2CO→CH2+CO) at 308 nm has been measured by using quantum-state-specific metastable time-of-flight (TOF) spectroscopy. This distribution is a matrix whose elements are the probability that if CO is produced in the dissociation with quantum-state ||nCO〉, CH2 will be produced with quantum-state ||nCH2〉. It was found that ketene photodissociation yields CH2 in three resolved states; the 1A1(000), and 1A1(010) states of CH2 are the major channels, while the 3B1 state is a minor channel. In addition to this scalar distribution, the vector correlations between the recoil velocity and the angular momentum of the CO fragment (v⋅j correlation), expressed by the β00(22) bipolar moment, have also been obtained as a function of the kinetic energy release of the photoreaction. The correlated product state distribution was found not to follow the predictions of phase space theory, suggesting that dynamic hindrances exist in the photoreaction that have not been previously observed. A phase space theory calculation with restricted impact parameter values was also performed and compared to experiment. The impact parameter restricted phase space theory more accurately reproduced all of the correlated product state information obtained in this work as well as previous uncorrelated product state distributions for CH2 and CO. Both the ranges and the values of the allowed impact parameters obtained from these restricted calculations increase as the rotational energy of CO increases. Also, the values of the allowed impact parameters for 1A1(010) CH2 are larger than for 1A1(000) CH2. This strongly suggests that C–C–O bending modes are hindered at the transition state and therefore play an important role in the photodissociation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471459
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  • 6
    Electronic Resource
    Electronic Resource
    The determination of the infrared radiative lifetimes of a vibrationally excited neutral molecule using stimulated-emission-pumping, molecular-beam time-of-flight (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3024-3028 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The authors present a new experimental method for measurement of collision-free infrared radiative lifetimes for single quantum states of a vibrationally excited sample. This method provides a more direct route to the infrared Einstein A coefficients than has been previously possible. Results for NO(X 2Π, v=21 and v=7) are presented. Comparison to results of ab initio calculations shows excellent agreement. A controversy regarding the relative intensities of first overtone and fundamental emission intensities in NO is laid to rest. The most complete least squares analysis of existing data was carried out to derive the electric dipole moment function (EDMF) to an accuracy of ±0.02 D between 0.9 and 1.7 Å. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473047
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  • 7
    Electronic Resource
    Electronic Resource
    State-specific neutral time-of-flight of CO from ketene photodissociation at 351 nm: The internal energy distribution of CH2(X˜ 3B1) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4550-4555 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Metastable time-of-flight (TOF) spectroscopy was used to measure the translational energy distribution of specific rotational states of CO formed from ketene photodissociation (CH2CO→CH2+CO) at 351 nm. This distribution could be directly related to the internal energy distribution of the other fragment (X˜ 3B1 CH2) formed in the reaction, thereby giving a correlated distribution of the internal states of the fragments. This technique overcomes the spectral complexity associated with detection the X˜ 3B1 state CH2. Previous measurements of the CO rotational distribution were simulated theoretically using the impulsive model and zero-point vibrational energy considerations. These models predicted that the rotational distributions of CO and CH2 should be uncorrelated, that ∼10% of the CH2 should be vibrationally excited with one quantum in the bending mode, and that the rotational energy distribution of CH2 should peak near zero. Measurements presented in this paper show a slight anticorrelation of CO and CH2 rotations, no vibrational excitation of CH2 and Gaussian-like rotational energy distributions of CH2 that peak at ∼1 kcal/mole and have a full width at half-maximum of ∼0.8 kcal/mol. Qualitative explanations for this behavior are presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472538
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational motion compensates the energy defect in near-resonant vibration–vibration energy transfer: A state-to-state study of NO(v)+N2O (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 355-358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Our lack of understanding of the factors that compensate energy defects in near resonant V–V energy transfer constrains our ability to accurately predict resonance widths and, thus, the overall importance of such processes. We have carried out one of the first truly state-to-state measurements of near resonant V–V energy transfer under single collision conditions, employing the crossed molecular beams, stimulated emission pumping technique. We have varied the energy defect ΔE for the process: NO X 2Π(v)+N2O(0,0,0)→NO X 2Π(v−1)+N2O(0,0,1), by changing the prepared vibrational state from v=22 (ΔE=+14 cm−1) to v=21 (ΔE=−18 cm−1) to v=20 (ΔE=−49 cm−1). Changes in the energy transfer efficiencies and rotational distributions of vibrationally inelastically scattered NO with energy defect both strongly suggest that molecular rotation (both of NO and N2O) is responsible for compensating the energy defect. Furthermore it appears that relative translation is ineffective in compensating the energy defect. A ΔJNO∼ΔJN20 approximation also appears valid. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476571
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of electric dipole moments and transition probabilities of low-lying singlet states of CO (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2352-2358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transitions from the X 1Σ+(v=0) ground state of the carbon monoxide molecule to the electronically excited A 1Π(v=0), B 1Σ+(v=0), and C 1Σ+(v=0) states have been studied by 2-photon laser induced fluorescence spectroscopy. Accurate molecular constants for the B and C state have been determined. The electric dipole moments for all three electronically excited states have been deduced from the observed Stark effects. The dipole moments for the A, B, and C states are found to be 0.335±0.013, 1.95±0.03, and 4.50±0.07 D, respectively. From the observed radiative lifetimes the transition probabilities of the B–A, B–X and C–B, C–A, and C–X transitions have been determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465250
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  • 10
    Electronic Resource
    Electronic Resource
    High resolution double-resonance spectroscopy on Rydberg states of CO (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5701-5711 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Rydberg states L 1Π(v=0), L' 1Π(v=1), K 1Σ+(v=0), W 1Π(v=0), and W' 1Π(v=2) have been studied in a 2+1 double-resonance detection scheme with a resolution of 0.005 cm−1. Accurate molecular constants have been derived for these states. From the observed linewidths of individual rotational transitions, predissociation rates for the Rydberg states have been deduced. For the first time a clear J and e/f dependence for the predissociation of CO has been observed. One of the states causing the observed predissociation could be identified as the D' 1Σ+ state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465919
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