Comment on “Selection rules for the photoionization of diatomic molecules” [J. Chem. Phys. 93, 3033 (1990)]

1998 ◽  
Vol 108 (2) ◽  
pp. 820-820 ◽  
Author(s):  
James K. G. Watson
Keyword(s):  
Diatomic Molecules ◽  
Chem Phys ◽  
Selection Rules

An alternative mechanism for spin-forbidden photo-ionization of diatomic molecules and its rotation–electronic selection rules

1990 ◽  
Vol 68 (2) ◽  
pp. 177-183 ◽  
Author(s):  
Ying-Nan Chiu ◽  
Lue-Yung Chow Chiu
Keyword(s):  
Diatomic Molecules ◽  
Rotational Level ◽  
Electric Quadrupole ◽  
Chem Phys ◽  
Electric Dipole Transition ◽  
Wave Functions ◽  
Alternative Mechanism ◽  
Selection Rules ◽  
Photon Ionization ◽  
Photo Ionization

The spin-forbidden photo-ionization of diatomic molecules is proposed. Spin orbit interaction is invoked resulting in the correction and mixing of the wave functions of different multiplicities. The rotation–electronic selection rules given, but not proven, by Dixit and McKoy for Hund's case a based on the conventional mechanism of electric dipole transition (see Chem. Phys. Lett. 128, 49 (1986) are rederived and expressed in a different format. This new format permits the generalization of the selection rules to other photo-ionization transitions caused by the magnetic dipole, the electric quadrupole, and the two- and three-photon operators. These selection rules, which are for transitions from one specific rotational level of a given Kronig reflection symmetry to another, will help understand rotational branching and the dynamics of interaction in the excited state. They will also help in the selective preparation of well-defined rovibronic states in resonant-enhanced multi-photon ionization processes.

Sub-Doppler Saturation Spectroscopy of HCN up to 1 THz and Detection of J = 3 —> 2 (4—> 3) Emission from TMC1

2002 ◽  
Vol 57 (8) ◽  
pp. 669-681 ◽  
Author(s):  
Volker Ahrens ◽  
Frank Lewen ◽  
Shuro Takano ◽  
Gisbert Winnewisser ◽  
Štepán Urban ◽  
...  
Keyword(s):  
Ground State ◽  
Rotational Transition ◽  
Chem Phys ◽  
Swiss Alps ◽  
Center Frequency ◽  
Rotational Spectrum ◽  
Molecular Constants ◽  
Emission Data ◽  
Selection Rules ◽  
Rotational Transitions

Very high-resolution ( ∼ 30 kHz) and very precise (±2 kHz) saturation dip and crossover dip measurements are reported for HCN. Nine consecutive rotational transitions of the vibrational ground state were recorded, covering the rotational spectrum up to the J = 11 ← 10 transition at 975 GHz. Commencing the saturation dip measurements with the J = 3 ← 2 transition located at 265 886.4 MHz, all rotational transitions were measured up to J = 11 ← 10 (ΔF = 1), positioned at a center frequency of 974 487.2 MHz. It has become possible to resolve the hyperfine structure of every rotational transition to varying degrees. Transitions obeying the selection rules ΔJ = 1, ΔF = 0 are have been resolved, those obeying the selection rules J = 1, F = 1 are only resolved for transitions lower than the J = 6 ← 5 transition.These new experimental saturation dip data, together with the molecular beam maser emission data of the J = 1 → 0 and J = 2 → 1 transitions reported by De Lucia and Gordy, (Phys. Rev. 187, 58 (1969)), and the recent terahertz measurements performed in this laboratory up to J = 22-21 at 1.946 THz (Maiwald et al., J. Mol. Spectrosc. 202, 166 (2000)), were subjected to a least squares analysis which yielded a highly precise set of molecular constants for the ground state of HCN: B = 44 315.974 970 (156) MHz, D = 0.087 216 35 (169) MHz, H = 0.086 96 (242) Hz; eQq = -4.709 03 (162) MHz, eQqJ = 0.244 (88) Hz, CN = 10.09 (38) kHz, CNJ = -0.0143 (86) mHz. Two constants, the hydrogen spin-rotation, CH = -4.35 (5) kHz, and the spin-spin interaction between the proton and nitrogen nucleus, SNH = 0.154 (3) kHz, can not be determined from the saturation dip measurements and have been taken from Ebenstein and Muenter, J. Chem. Phys. 80, 3989 (1984). There also a value for the ground state permanent electric dipole moment (in Debye’s) is given, which we quote for completeness: 〈μ〉000 = 2.985 188 (3) D. We also report the discovery of the J = 3 → 2 and J = 4 → 3 ground state rotational transitions of HCN in the dark, cold molecular cloud TMC1 by using the KOSMA 3m-Submillimeter Telescope located in the central Swiss Alps. For the J = 3 → 2 transition the hyperfine splitting has partly been resolved. The intensities of the hyperfine components are anomalous, and they are not in thermodynamic equilibrium.

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