C2H2 Results

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Results and dicussion

The vibrational bands of the E−X transition have been reassigned to the nν₃ and ν₂+nν₃ progressions. [normal modes of C₂H₂]

The predissociation rates from the D and F Rydberg states are accelerated by the C−H anti-symmetric stretch.

The level energies and the homogeneous bandwidths, which correspond to the predissociation rates, of the observed vibronic states of acetylene in the D, E, and F states have been determined in the present study. [graph]

Energies of peak positions and their Lorentzian widths.
State Assignment Wavenumber
/cm⁻¹ Vibrational
energy /cm⁻¹ Full width at half
Maximum /cm⁻¹

D 0 74490.2(1) 0 58.9(4)

2¹ 76270^a 1780 87^a

3¹ 77629(3) 3139(3) 184(13)

1¹3¹ 80677(5) 6187(5) 139(19)

E 3² 74029(1) 1276^b 50(4)

3³ 74614.5(3) 1861.5^b 26(1)

2¹3¹ 75011(1) 2258^b 40(4)

3⁴ 75243(1) 2490^b 55(5)

2¹3² 75580 2827^b

3⁵ 75850^a 3097^b 37^a

2¹3³ 76100^a 3347^b 43^a

F 0 74751.4(1) 0 66.7(2)

2¹ 76480^a 1729 53^a

3¹ 77817(3) 3066(3) 103(5)

1¹3¹ 80944(3) 6193(3) 149(14)

^aP. Löffler et al., Chem. Phys. Lett. 252, 304 (1996); P. Löffler et al., J. Chem. Phys. 109, 5231 (1998)
^bThe origin band is 72753 cm⁻¹ (Ref. M.N.R. Ashfld et al., J. Chem. Phys. 87, 5105 (1987)

The quantum yield for the production of C₂H(A,B) fragment through the D ¹Π_u Rydnerg state is larger than through the F ¹Σ_u⁺ Rydberg state.

The predissociation process through the origin of D and F Rydberg states have comparable rates, while that through the E¹Avalence state is slower. [graph]

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