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Title

Electronic Spectra and Structures of Solvated NH4 Radicals, NH4(NH3)n (n = 1 - 8)

Shinji Nonose a), Tomokazu Taguchi a), Feiwu Chen b,c) , Suehiro Iwatac,d), and Kiyokazu Fuke a)

a)Department of Chemistry, Faculty of Science, Kobe University, Kobe 657-8501, Japan

b)Japan Science and Technology Corporation, Japan

c) Institute of Molecular Science, Okazaki 444-8585, Japan

d)Evaluation of University Education and Research, NIAD, Chiyoda, Tokyo, 101-8436, Japan

Abstract

NH4(NH3)nproduced through the photolysis of ammonia clusters

Photodepletion spectroscopy of NH4(NH3)n

derived from 3p-3s excitation of NH4

1. Vibrationaly resolved spectrum of NH4NH3

(9000 - 12000 cm-1)

2. Electronic spectra of NH4(NH3)n(n = 1 - 8)

(4500 - 16000 cm-1 )

Schematic of Set up for Dual Beam Configuration

(NH3)n NH4(NH3)m +NH2 +(n-m-2)NH3

Absorption Spectra of NH4NH3 at Various Delay Time between n1 and n2

Absorption Cross Section(a. u.)

Wavenumber / 1000 cm-1

Absorption Spectrum of NH4NH3 (9000 - 12000 cm-1)

Absorption Cross Section(a. u.)

0

500

1000

1500

2000

Wavenumber / cm-1

Adiabatic Energy Diagram of NH4 and NH4NH3

Electronic Character of 3p States of NH4NH3

3p() state, 12E

3p() state, 22A

Table 2. Theoretical and experimental vibrational frequencies of NH4NH3

Assignment of Absorption Spectrum of NH frequencies of NH4NH3 (9000 - 12000 cm-1)

Absorption Cross Section(a. u.)

0

500

1000

1500

2000

Wavenumber / cm-1

Absorption Spectra of NH frequencies of NH4(NH3 ) n (n = 1 - 8) (4500 - 16000 cm-1)

Absorption Cross Section(a. u.)

Wavenumber / 1000 cm-1

Intermolecular Potential frequencies of NHCurves of NH4NH3

Determination of the successive binding energies Dn-1,n[NH4(NH3)n-1 - NH3]

Energy (eV)

J. D. Payzant, A. J. Cunnungham, P. Kebarle, Can. J. Chem., 51, 3242 (1973).

K. Fuke, R. Takasu, F. Misaizu, Chem. Phys. Lett., 229, 597 (1994).

NH4-NH3Distance

Summary frequencies of NH

- 1. Vibronic Spectrum of NH4NH3
- Band Origin of 22A State 9305 cm-1
- Band Origin of 12E State 10073 cm-1
- Excitation of Intermolecular Bending Vibrations

- 2. Electronic Absorption Spectra of NH4(NH3)n(n = 1-8)
- 3p-3s Transition of NH4
- First Solvation Shell Closing at NH4(NH3)4
- Spontaneous Ionization of NH4 in Clusters

Table 1. The geometric parameters, the binding energy frequencies of NHE and the barrier height of H3NHNH3

Intermolecular Vibrational Modes of NH frequencies of NH4NH3

Table 3. band positions in 2 frequencies of NH2A – 12A and 12E – 12A transition of NH4NH3

Band Positions in 22A – 12A and 12E – 12A

Transition of NH4NH3

Ionization Potential and Absorption Maximum of NH frequencies of NH4(NH3)n

Abstract.org frequencies of NH

Abstract

Electronic spectra of ammoniated ammonium radicals, NH4(NH3)n,produced through the photolysis of ammonia clusters, are investigated with a laser photodepletion spectroscopy.Vibrationaly resolved bands beginning at energy of 9305 ± 15 cm-1 are successfully assigned to NH4NH3. These bands are ascribed to the 2 2A —1 2A transition derived from the 3p2F2-3s2A1 excitation of NH4. A second group of bands beginning at energy 10073 ± 15 cm-1 is assigned to the 12E -12A transition. Electronic spectra of a series of NH4(NH3)n(n = 1 - 8) are also recorded with low resolution in the energy region of 4500 - 16000 cm-1. A drastic decrease of the excitation energy from 15062 cm-1 for NH4 to 5800 cm-1 for NH4(NH3)4 is observed, while no appreciable spectral change is found for n 5. The large spectral change is ascribed to the spontaneous ionization of NH4 in ammonia clusters. Successive binding energies of NH4(NH3)nin the excited state are determined from the spectral band positions.

Vibrational frequency (cm frequencies of NH-1)

NH3symmetric stretching A1 3337

symmetric bending A1 950

asymmetric stretching E 3444

symmetric bending A1 1627

NH4+symmetric stretching A1 3042

bending E 1711

asymmetric stretching F2 3135

bending F2 1403

NH4symmetric stretching A1 2552

bending E 1581

G. Herzberg, J. Astrophys., 5, 131 (1984).