Photodissociation and ionisation rates

The calculation of photodissociation and ionisation rate of atoms and molecules when exposed to interstellar ultraviolet radiation is discussed in various overview papers. Briefly, a rate (k, s-1) is calculated assuming different kinds of wavelength (λ, nm) dependent ultraviolet radiation fields (I, photons s-1 nm-1) according to the integral:

k = ∫σ(λ)×I(λ) dλ

where σ(λ) is the continuum photodissociation or ionisation cross section (cm2) as a function of wavelength. In some cases we have listed photoabsorption lines with integrated cross sections (σint, cm2 cm-1) and absorption wavelengths (λ0). These lines contribute to the photodestruction rates, along with the continuum part, so that:

k = Σ σint×I(λ0) + ∫σ(λ)×I(λ) dλ

The various kinds of interstellar radiation fields considered are explained here.

Click on a link below to get rates for that atom or molecule.

Al AlH C C2 C2H C2H2 C2H4 C2H5OH
C2H6 C3 C3H7OH CH CH+ CH2 CH2+ CH3
CH3CHO CH3CN CH3NH2 CH3OH CH3SH CH4 CH4+ CN
CO CO+ CO2 CS CS2 Ca Ca+ Cl
Co Cr Fe H H- H2 H2+ H2CO
H2O H2O2 H2S HC3H HC3N HCN HCO HCO+
HCl HCl+ HF HO2 K Li LiH Mg
MgH Mn N N2 N2O NH NH+ NH2
NH2CHO NH3 NO NO2 Na NaCl NaH Ni
O O2 O2+ O3 OCS OH OH+ P
PH PH+ Rb S S2 SH SH+ SO
SO2 Si SiH SiH+ SiO Ti Zn c-C3H
c-C3H2 l-C3H l-C3H2 l-C4 l-C4H l-C5H

Tabulated photodestruction rates for all atoms and molecules

[Download all rates in a csv file.]

In units per second (s-1).

Photodestruction products

Below we provide rates photodissociation and ionisation separately. That is, the sum of dissociation or dissociative-ionisation product channels. The dominant photodissociation and ionisation products at their threshold wavelengths are given on the cross sections page.

Uncertainties

Uncertainties are estimated from the known or approximate uncertainties of the measured and experimental cross sections compiled for each atom or molecule. These are estimated over the wavelength ranges relevant to cosmic ray generated radiation (80 to 150 nm). These are categorised as follows:

Species ProductsISRFMathis4000K10000K20000KLyman-alphaSolarTW-Hya Uncertainty
Al photoionisation4.39e-092.98e-092.15e-081.00e-085.33e-091.37e-092.14e-083.67e-09B
AlH photodissociation2.63e-101.86e-104.00e-091.07e-093.80e-100.00e+005.28e-092.35e-10C
AlH photoionisation1.51e-109.88e-111.25e-125.58e-111.26e-103.38e-101.44e-112.29e-10C
C photoionisation3.39e-102.55e-105.69e-152.81e-112.96e-100.00e+009.92e-128.34e-11B
C2 photodissociation2.35e-101.72e-104.61e-134.47e-112.15e-107.83e-117.41e-129.22e-11B
C2 photoionisation4.09e-103.42e-101.39e-152.75e-114.18e-100.00e+006.71e-128.75e-11B
C2H photodissociation1.58e-091.04e-094.42e-116.76e-101.34e-095.08e-106.44e-118.34e-10B
C2H2 photodissociation2.41e-091.58e-091.28e-101.08e-092.05e-098.67e-094.22e-103.17e-09A+
C2H2 photoionisation5.28e-104.15e-105.21e-154.01e-114.91e-100.00e+002.39e-111.67e-10A+
C2H4 photodissociation3.06e-092.04e-097.53e-102.44e-092.96e-093.71e-097.94e-103.51e-09C
C2H4 photoionisation4.10e-103.20e-101.64e-143.73e-113.71e-100.00e+006.19e-128.10e-11C
C2H5OH photodissociation2.48e-091.69e-092.13e-109.19e-102.12e-094.02e-093.67e-103.04e-09A
C2H5OH photoionisation4.86e-103.85e-101.43e-144.12e-114.48e-106.76e-182.81e-111.76e-10A
C2H6 photodissociation2.13e-091.46e-095.93e-124.77e-101.73e-093.56e-091.59e-102.49e-09A+
C2H6 photoionisation2.25e-102.03e-107.86e-161.50e-112.38e-100.00e+002.31e-111.19e-10A+
C3 photodissociation4.97e-093.19e-096.53e-104.34e-094.93e-092.17e-095.85e-104.17e-09C
C3 photoionisation1.36e-101.15e-109.03e-169.67e-121.36e-100.00e+003.55e-123.33e-11C
C3H7OH photodissociation4.03e-092.72e-093.79e-101.54e-093.40e-098.12e-096.81e-105.77e-09A
C3H7OH photoionisation7.65e-106.05e-102.63e-146.56e-117.04e-104.40e-114.30e-112.91e-10A
CH photodissociation9.14e-106.35e-101.73e-072.21e-099.58e-107.87e-122.13e-071.13e-09C
CH photoionisation7.63e-105.59e-102.26e-146.82e-116.42e-100.00e+009.64e-121.38e-10C
CH+ photodissociation3.29e-102.58e-105.99e-103.79e-113.16e-107.87e-128.12e-108.07e-11A
CH2 photodissociation5.80e-103.90e-102.96e-091.28e-096.97e-107.87e-123.46e-093.70e-10C
CH2+ photodissociation1.41e-101.16e-103.74e-118.33e-111.55e-107.87e-123.43e-114.66e-11B
CH3 photodissociation6.23e-104.02e-102.59e-097.45e-106.14e-102.57e-714.34e-092.33e-10B
CH3 photoionisation3.28e-102.35e-108.58e-144.48e-112.66e-108.36e-103.61e-115.52e-10B
CH3CHO photodissociation1.99e-091.30e-093.78e-091.58e-091.89e-093.19e-094.82e-092.66e-09A
CH3CHO photoionisation8.34e-106.05e-108.25e-149.37e-116.83e-101.93e-102.36e-112.82e-10A
CH3CN photodissociation2.95e-092.06e-099.10e-125.37e-102.40e-091.71e-091.09e-101.64e-09A
CH3CN photoionisation1.20e-101.11e-103.77e-167.85e-121.32e-100.00e+001.56e-117.75e-11A
CH3NH2 photodissociation7.26e-104.75e-104.22e-091.28e-098.02e-109.83e-166.29e-094.26e-10A
CH3NH2 photoionisation1.60e-091.15e-096.93e-132.31e-101.32e-093.83e-091.73e-102.55e-09A
CH3OH photodissociation1.38e-099.46e-101.23e-105.34e-101.19e-092.18e-092.11e-101.65e-09A+
CH3OH photoionisation3.11e-102.45e-105.48e-152.52e-112.84e-100.00e+001.65e-111.07e-10A+
CH3SH photodissociation2.80e-091.84e-097.38e-092.80e-092.70e-093.43e-098.46e-093.11e-09A
CH3SH photoionisation1.91e-091.34e-098.13e-132.86e-101.52e-093.72e-091.61e-102.51e-09A
CH4 photodissociation1.52e-091.08e-091.68e-122.67e-101.27e-092.84e-091.28e-101.95e-09A+
CH4 photoionisation1.03e-111.24e-119.34e-185.55e-131.16e-113.29e-259.34e-123.81e-11A+
CH4+ photodissociation2.77e-101.91e-101.74e-134.62e-112.20e-107.87e-123.64e-125.22e-11B
CN photodissociation5.19e-104.25e-102.33e-145.11e-114.53e-102.04e-111.65e-111.26e-10B
CN photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+002.03e-125.88e-12B
CO photodissociation2.43e-102.12e-102.81e-151.81e-112.38e-100.00e+001.02e-115.72e-11A+
CO photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+006.52e-122.54e-11A+
CO+ photodissociation1.04e-107.12e-111.68e-132.40e-118.35e-117.87e-121.42e-122.29e-11B
CO2 photodissociation1.02e-097.79e-102.37e-121.14e-108.99e-101.03e-112.17e-112.15e-10A+
CO2 photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+006.52e-122.57e-11A+
CS photodissociation9.49e-106.29e-105.20e-122.90e-107.64e-108.42e-093.09e-104.95e-09C
CS photoionisation2.60e-111.84e-117.27e-162.41e-122.10e-110.00e+001.89e-133.62e-12C
CS2 photodissociation8.80e-096.15e-095.01e-081.93e-081.04e-082.69e-095.13e-086.68e-09A
CS2 photoionisation3.56e-102.63e-102.04e-143.44e-113.03e-101.63e-102.07e-112.03e-10A
Ca photoionisation3.47e-102.32e-108.00e-106.18e-103.98e-101.44e-107.90e-102.91e-10B
Ca+ photoionisation2.45e-121.96e-121.30e-171.73e-132.37e-120.00e+005.24e-145.98e-13B
Cl photoionisation4.74e-115.49e-114.49e-172.53e-125.13e-110.00e+001.15e-114.91e-11B
Co photoionisation5.34e-113.44e-113.33e-123.67e-115.03e-112.78e-113.50e-124.47e-11B
Cr photoionisation1.58e-091.06e-091.75e-092.14e-091.70e-091.16e-091.88e-091.42e-09B
Fe photoionisation4.71e-103.10e-101.20e-112.10e-104.10e-107.67e-103.90e-115.90e-10A
H photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+001.64e-125.45e-12A
H- photoionisation1.46e-071.57e-081.63e-032.46e-071.39e-087.48e-101.45e-052.26e-06B
H2 photodissociation5.68e-114.60e-112.02e-163.86e-125.77e-110.00e+003.08e-121.68e-11A+
H2 photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+004.88e-133.21e-12A+
H2+ photodissociation5.72e-103.88e-104.28e-112.01e-104.83e-101.07e-098.74e-117.63e-10A
H2CO photodissociation1.42e-099.55e-103.98e-099.58e-101.33e-091.49e-095.10e-091.41e-09B
H2CO photoionisation3.96e-103.07e-101.10e-143.49e-113.58e-100.00e+001.31e-111.05e-10B
H2O photodissociation7.72e-105.31e-101.57e-104.61e-107.14e-102.41e-092.30e-101.64e-09A+
H2O photoionisation2.71e-112.65e-114.26e-171.71e-123.14e-110.00e+004.25e-122.18e-11A+
H2O2 photodissociation8.08e-105.34e-102.41e-095.51e-107.16e-101.52e-092.90e-091.13e-09A
H2O2 photoionisation2.48e-102.02e-103.20e-151.89e-112.37e-100.00e+001.19e-117.67e-11A
H2S photodissociation3.12e-092.08e-094.24e-092.19e-092.82e-098.35e-096.13e-094.45e-09A
H2S photoionisation7.81e-105.89e-104.58e-147.78e-116.69e-100.00e+002.64e-112.02e-10A
HC3H photodissociation2.15e-091.47e-091.80e-076.55e-092.65e-097.87e-122.95e-072.23e-09B
HC3N photodissociation7.13e-094.67e-096.23e-103.49e-096.28e-093.12e-099.63e-103.83e-09A
HC3N photoionisation2.28e-101.84e-101.34e-151.62e-112.21e-100.00e+001.19e-117.72e-11A
HCN photodissociation1.64e-091.16e-095.73e-122.81e-101.32e-095.35e-092.10e-103.26e-09A
HCN photoionisation4.39e-137.08e-134.64e-204.22e-159.83e-140.00e+007.46e-122.79e-11A
HCO photodissociation1.10e-094.85e-105.00e-062.75e-098.77e-101.16e-111.66e-087.41e-09C
HCO+ photodissociation5.39e-123.74e-121.13e-164.92e-134.16e-120.00e+002.82e-147.25e-13B
HCl photodissociation1.73e-091.20e-099.35e-115.06e-101.47e-091.46e-101.08e-105.59e-10A
HCl photoionisation4.45e-114.31e-116.75e-172.82e-125.20e-110.00e+001.18e-115.12e-11A
HCl+ photodissociation1.09e-108.50e-111.03e-122.36e-111.04e-101.33e-107.89e-121.05e-10C
HCl+ photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+000.00e+000.00e+00C
HF photodissociation1.38e-109.85e-115.31e-132.88e-111.17e-104.93e-102.18e-113.19e-10A
HF photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+002.45e-132.13e-12A
HO2 photodissociation6.69e-104.43e-101.79e-082.02e-097.93e-107.87e-122.20e-084.83e-10C
K photoionisation3.89e-112.60e-113.67e-105.88e-114.02e-113.50e-114.17e-104.03e-11B
Li photoionisation3.45e-102.30e-103.07e-097.06e-103.86e-102.09e-104.90e-093.30e-10A
LiH photodissociation4.89e-092.98e-092.11e-063.25e-084.67e-097.87e-122.22e-068.43e-09A
Mg photoionisation6.59e-114.29e-118.13e-125.35e-116.42e-111.12e-117.28e-124.19e-11B
MgH photodissociation5.07e-103.27e-102.36e-088.78e-105.27e-107.87e-123.18e-082.71e-10C
Mn photoionisation3.34e-112.15e-116.83e-123.35e-113.42e-116.96e-125.78e-122.58e-11B
N photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+001.63e-127.82e-12A
N2 photodissociation1.70e-101.52e-103.18e-161.10e-111.91e-100.00e+001.05e-115.24e-11A+
N2 photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+001.31e-128.79e-12A+
N2O photodissociation1.87e-091.25e-092.89e-115.13e-101.52e-096.06e-107.01e-117.31e-10B
N2O photoionisation1.73e-101.91e-101.83e-161.05e-112.12e-100.00e+003.81e-123.74e-11B
NH photodissociation5.75e-103.78e-101.06e-112.39e-105.06e-104.88e-111.66e-111.74e-10B
NH photoionisation1.90e-122.95e-120.00e+000.00e+000.00e+000.00e+002.76e-121.02e-11B
NH+ photodissociation5.30e-113.60e-111.19e-081.96e-104.92e-117.36e-128.44e-095.86e-11C
NH2 photodissociation9.51e-106.27e-105.47e-101.29e-091.04e-094.76e-124.34e-104.35e-10C
NH2 photoionisation1.90e-101.51e-101.66e-151.41e-111.80e-100.00e+008.71e-125.79e-11C
NH2CHO photodissociation2.70e-091.79e-092.35e-093.10e-092.78e-092.87e-092.73e-093.04e-09A
NH2CHO photoionisation5.17e-104.00e-102.75e-144.94e-114.58e-102.95e-111.99e-111.55e-10A
NH3 photodissociation1.44e-099.87e-103.63e-091.71e-091.43e-091.32e-094.08e-091.40e-09A+
NH3 photoionisation2.69e-101.97e-101.75e-142.79e-112.23e-104.75e-119.57e-129.01e-11A+
NO photodissociation3.84e-102.72e-102.10e-103.14e-103.87e-107.53e-112.14e-102.18e-10A
NO photoionisation2.60e-101.93e-107.36e-143.07e-112.25e-103.27e-101.93e-112.58e-10A
NO2 photodissociation1.39e-099.22e-104.84e-101.13e-091.33e-097.87e-124.13e-101.30e-09B
NO2 photoionisation1.54e-101.19e-104.22e-151.29e-111.39e-101.67e-113.09e-124.13e-11B
Na photoionisation1.36e-119.09e-121.29e-101.48e-111.27e-111.68e-111.38e-101.55e-11B
NaCl photodissociation9.45e-106.02e-106.00e-083.64e-091.18e-097.87e-126.13e-088.44e-10C
NaH photodissociation7.00e-094.46e-093.70e-064.59e-086.41e-097.87e-123.97e-061.29e-08A
Ni photoionisation9.76e-116.30e-119.50e-127.52e-119.39e-114.90e-119.54e-127.71e-11B
O photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+001.38e-126.21e-12B
O2 photodissociation7.51e-104.88e-107.32e-115.50e-107.23e-102.02e-126.10e-113.44e-10A
O2 photoionisation4.89e-114.29e-111.26e-163.23e-125.34e-110.00e+003.49e-122.25e-11A
O2+ photodissociation3.46e-112.29e-111.43e-113.88e-113.55e-113.96e-102.43e-112.49e-10B
O3 photodissociation1.83e-091.15e-092.36e-075.80e-091.75e-094.66e-092.22e-074.10e-09B
O3 photoionisation3.32e-113.40e-114.35e-172.06e-123.95e-110.00e+007.47e-123.47e-11B
OCS photodissociation4.67e-093.06e-091.64e-093.79e-094.55e-091.15e-091.81e-093.66e-09A
OCS photoionisation7.67e-106.06e-101.13e-146.07e-117.30e-100.00e+003.01e-112.18e-10A
OH photodissociation3.79e-102.54e-101.91e-102.01e-103.34e-106.40e-101.70e-105.05e-10A
OH+ photodissociation1.30e-111.12e-114.38e-139.55e-131.30e-115.32e-176.82e-132.90e-12A
P photoionisation1.89e-091.37e-091.39e-132.05e-101.55e-090.00e+003.27e-113.63e-10C
PH photodissociation5.78e-103.77e-106.83e-114.20e-105.43e-101.79e-115.85e-113.20e-10C
PH+ photodissociation1.40e-101.09e-109.59e-084.08e-101.07e-101.67e-108.01e-083.08e-10C
Rb photoionisation2.74e-111.84e-111.62e-094.79e-112.72e-112.34e-112.21e-093.00e-11B
S photoionisation1.13e-098.43e-108.09e-141.15e-109.75e-100.00e+002.43e-112.30e-10A
S2 photodissociation6.56e-103.74e-101.98e-074.27e-096.66e-100.00e+002.07e-071.01e-09B
S2 photoionisation1.28e-109.25e-116.46e-141.76e-111.06e-102.83e-101.33e-111.98e-10B
SH photodissociation1.23e-098.09e-103.42e-082.82e-091.38e-091.27e-094.95e-081.54e-09B
SH photoionisation5.02e-113.71e-115.30e-163.86e-124.50e-110.00e+008.86e-131.10e-11B
SH+ photodissociation6.86e-105.18e-103.98e-083.22e-106.08e-101.17e-114.64e-082.42e-10B
SH+ photoionisation0.00e+000.00e+000.00e+000.00e+000.00e+000.00e+000.00e+000.00e+00B
SO photodissociation4.25e-092.85e-098.44e-093.03e-093.68e-091.67e-081.23e-081.10e-08B
SO photoionisation5.31e-103.69e-103.22e-145.66e-114.07e-109.41e-176.56e-129.77e-11B
SO2 photodissociation2.47e-091.69e-094.00e-091.75e-092.22e-096.08e-095.55e-094.33e-09A
SO2 photoionisation1.31e-101.23e-102.73e-168.36e-121.45e-100.00e+001.66e-118.41e-11A
Si photoionisation4.47e-092.94e-099.29e-112.04e-093.91e-095.69e-092.90e-104.38e-09B
SiH photodissociation2.71e-091.84e-091.14e-061.48e-083.00e-097.87e-121.03e-065.19e-09B
SiH+ photodissociation2.59e-092.65e-095.40e-061.13e-081.49e-093.50e-094.21e-061.14e-08A
SiO photodissociation1.59e-091.04e-091.41e-116.05e-101.36e-097.87e-121.47e-113.46e-10B
Ti photoionisation2.39e-101.64e-109.77e-127.70e-112.02e-104.18e-102.60e-112.94e-10C
Zn photoionisation4.10e-102.85e-103.08e-143.76e-113.23e-109.23e-123.03e-126.69e-11B
c-C3H photodissociation1.06e-096.47e-101.10e-073.77e-091.14e-097.87e-121.32e-071.14e-09B
c-C3H2 photodissociation1.39e-098.77e-105.54e-083.27e-091.51e-097.87e-122.96e-088.54e-10B
l-C3H photodissociation1.77e-091.25e-094.70e-074.41e-091.97e-097.87e-124.17e-072.12e-09B
l-C3H2 photodissociation4.13e-092.68e-096.68e-093.65e-093.89e-092.29e-097.25e-093.13e-09B
l-C4 photodissociation8.48e-095.67e-095.42e-082.22e-081.10e-087.87e-128.35e-085.54e-09B
l-C4H photodissociation3.66e-092.34e-097.45e-103.30e-093.66e-097.87e-126.75e-101.23e-09B
l-C5H photodissociation1.30e-099.36e-106.87e-077.97e-091.30e-097.87e-129.62e-072.35e-09B